feat(welcome): landing lightbox, prod-served screenshots & session-end UX

- Serve real files at the SPA root (e.g. /welcome/*.png, favicon) from the built app — the
  landing screenshots were only ever shown by the Vite dev server, never in production.
- Add the Channel-manager screenshot; the two secondary previews are smaller thumbnails that
  open in a custom full-size lightbox (fit-to-viewport, Esc/backdrop/✕ to close).
- Drop a suspended/deleted user to the login page on the next 401 (and poll the session only
  while signed in, so the public login page no longer flickers); 'suspended' and 'account
  deleted' confirmation banners; strip redirect query params for a clean address bar.

backend/app/main.py

@@ -107,4 +107,11 @@ async def spa_fallback(full_path: str) -> FileResponse:
     # Client-side routes fall back to index.html; real API/asset paths are matched above.
     if full_path.startswith(("api/", "auth/", "healthz", "assets/")):
         raise HTTPException(status_code=404)
+    # Serve real files that live at the SPA root (Vite copies public/ there — e.g. the landing
+    # screenshots under /welcome/, favicon). /assets is already mounted above; everything else
+    # that isn't a real file is a client-side route → index.html. Guard against path traversal.
+    if full_path:
+        candidate = (STATIC_DIR / full_path).resolve()
+        if candidate.is_file() and STATIC_DIR.resolve() in candidate.parents:
+            return FileResponse(candidate)
     return FileResponse(STATIC_DIR / "index.html")

frontend/src/App.tsx

@@ -1,7 +1,7 @@
 import { useCallback, useEffect, useRef, useState } from "react";
 import { useTranslation } from "react-i18next";
-import { useQuery } from "@tanstack/react-query";
-import { api, HttpError, type FeedFilters } from "./lib/api";
+import { useQuery, useQueryClient } from "@tanstack/react-query";
+import { api, HttpError, setUnauthorizedHandler, type FeedFilters } from "./lib/api";
 import { setLanguage, isSupported, type LangCode } from "./i18n";
 import {
   applyTheme,
@@ -264,7 +264,47 @@ export default function App() {
     return () => window.removeEventListener("popstate", onPop);
   }, []); // eslint-disable-line react-hooks/exhaustive-deps
 
-  const meQuery = useQuery({ queryKey: ["me"], queryFn: api.me });
+  const queryClient = useQueryClient();
+  // Poll the session so an account suspended/deleted by an admin is noticed even with no
+  // interaction (option 1): the refetch 401s → the 401 handler below drops to the login page.
+  // Only poll while signed in (data present) — polling on the public login page is pointless and
+  // its periodic refetch caused a visible flicker there.
+  const meQuery = useQuery({
+    queryKey: ["me"],
+    queryFn: api.me,
+    refetchInterval: (query) => (query.state.data ? 60_000 : false),
+  });
+
+  // Any request that 401s means the session ended server-side. If we were signed in (cached
+  // `me` exists), reload to the login page at once (option 2 — also covers any click that hits
+  // the API). Guarded on cached `me` so the public login page's own /api/me 401 can't loop.
+  useEffect(() => {
+    setUnauthorizedHandler(() => {
+      if (queryClient.getQueryData(["me"])) {
+        queryClient.clear();
+        window.location.reload();
+      }
+    });
+    return () => setUnauthorizedHandler(null);
+  }, [queryClient]);
+
+  // Returning from an in-app Google link/upgrade round-trip (auth.py redirects to ?link=…).
+  // Surface the outcome, refresh `me` (can_read/can_write/has_google may have flipped), land on
+  // Settings → Account so the new state is visible, then strip the param for a clean URL.
+  useEffect(() => {
+    const result = new URLSearchParams(window.location.search).get("link");
+    if (!result) return;
+    if (result === "ok") {
+      notify({ level: "success", message: t("settings.account.googleLink.linked") });
+      void meQuery.refetch();
+      localStorage.setItem("siftlode.settingsTab", "account");
+      setPage("settings");
+    } else {
+      const key = result === "conflict" || result === "mismatch" ? result : "error";
+      notify({ level: "error", message: t(`settings.account.googleLink.${key}`) });
+    }
+    stripUrlParams();
+  }, []); // eslint-disable-line react-hooks/exhaustive-deps
 
   // First-login onboarding: prompt the user to connect YouTube (and resume the flow after
   // each consent redirect). Derived from granted scopes + storage flags so it's stable

frontend/src/components/Welcome.tsx

@@ -1,12 +1,14 @@
-import { useState } from "react";
+import { useEffect, useState } from "react";
 import { useTranslation } from "react-i18next";
 import {
+  Expand,
   Filter,
   Inbox,
   ListVideo,
   Lock,
   PlayCircle,
   Tags,
+  X,
   type LucideIcon,
 } from "lucide-react";
 import { api } from "../lib/api";
@@ -25,6 +27,9 @@ type Mode = "signin" | "register" | "forgot" | "reset";
 // backend); errors are surfaced inline (the api calls use the quiet flag).
 export default function Welcome() {
   const { t, i18n } = useTranslation();
+  // Which screenshot (if any) is open in the full-size lightbox.
+  const [zoomed, setZoomed] = useState<{ src: string; label: string } | null>(null);
+  const open = (src: string, label: string) => setZoomed({ src, label });
   return (
     <div className="min-h-screen bg-bg text-fg overflow-y-auto">
       <header className="flex items-center justify-between px-5 sm:px-8 py-4">
@@ -48,7 +53,12 @@ export default function Welcome() {
         </section>
 
         {/* App preview */}
-        <Preview src="/welcome/feed.png" label={t("welcome.preview.feed")} className="aspect-video" />
+        <Preview
+          src="/welcome/feed.png"
+          label={t("welcome.preview.feed")}
+          className="aspect-video"
+          onOpen={open}
+        />
 
         {/* Features */}
         <section className="mt-14">
@@ -60,13 +70,27 @@ export default function Welcome() {
           </div>
         </section>
 
-        {/* Secondary showcase */}
-        <section className="grid sm:grid-cols-2 gap-4 mt-12">
-          <Preview src="/welcome/channels.png" label={t("welcome.preview.channels")} className="aspect-[4/3]" />
-          <Preview src="/welcome/playlists.png" label={t("welcome.preview.playlists")} className="aspect-[4/3]" />
+        {/* Secondary showcase — smaller thumbnails; click to view full size. */}
+        <section className="mt-12 flex flex-wrap justify-center gap-4">
+          <Preview
+            src="/welcome/channels.png"
+            label={t("welcome.preview.channels")}
+            className="w-full sm:w-72 aspect-[4/3]"
+            onOpen={open}
+          />
+          <Preview
+            src="/welcome/playlists.png"
+            label={t("welcome.preview.playlists")}
+            className="w-full sm:w-72 aspect-[4/3]"
+            onOpen={open}
+          />
         </section>
       </main>
 
+      {zoomed && (
+        <Lightbox src={zoomed.src} label={zoomed.label} onClose={() => setZoomed(null)} />
+      )}
+
       <footer className="border-t border-border py-6 text-center text-xs text-muted flex flex-col sm:flex-row gap-3 justify-center items-center">
         <span>
           Sift<span className="text-accent">lode</span>
@@ -107,33 +131,112 @@ function FeatureCard({ icon: Icon, k }: { icon: LucideIcon; k: string }) {
 
 // Image with a graceful fallback: if the file isn't present yet, show a tasteful placeholder
 // frame instead of a broken image (the demo screenshots drop into frontend/public/welcome/).
-function Preview({ src, label, className }: { src: string; label: string; className?: string }) {
+// When loaded it's a button that opens the full-size lightbox (onOpen).
+function Preview({
+  src,
+  label,
+  className,
+  onOpen,
+}: {
+  src: string;
+  label: string;
+  className?: string;
+  onOpen?: (src: string, label: string) => void;
+}) {
   const [failed, setFailed] = useState(false);
-  return (
-    <div className={`glass-card rounded-2xl overflow-hidden ${className ?? ""}`}>
-      {failed ? (
+  if (failed) {
+    return (
+      <div className={`glass-card rounded-2xl overflow-hidden ${className ?? ""}`}>
         <div className="w-full h-full grid place-items-center bg-gradient-to-br from-accent/10 to-card text-muted text-sm p-6 text-center">
           {label}
         </div>
-      ) : (
+      </div>
+    );
+  }
+  return (
+    <button
+      type="button"
+      onClick={() => onOpen?.(src, label)}
+      aria-label={label}
+      className={`group relative glass-card rounded-2xl overflow-hidden block cursor-zoom-in ${className ?? ""}`}
+    >
+      <img
+        src={src}
+        alt={label}
+        loading="lazy"
+        onError={() => setFailed(true)}
+        className="w-full h-full object-cover object-top"
+      />
+      <span className="absolute inset-0 grid place-items-center bg-black/0 opacity-0 transition group-hover:bg-black/30 group-hover:opacity-100">
+        <Expand className="w-6 h-6 text-white drop-shadow-lg" />
+      </span>
+    </button>
+  );
+}
+
+// Full-size image viewer: a dimmed, blurred backdrop with the screenshot fit to the viewport
+// (aspect ratio preserved via object-contain). Closes on backdrop click, the ✕, or Escape.
+function Lightbox({ src, label, onClose }: { src: string; label: string; onClose: () => void }) {
+  useEffect(() => {
+    const onKey = (e: KeyboardEvent) => {
+      if (e.key === "Escape") onClose();
+    };
+    window.addEventListener("keydown", onKey);
+    const prev = document.body.style.overflow;
+    document.body.style.overflow = "hidden"; // no background scroll while open
+    return () => {
+      window.removeEventListener("keydown", onKey);
+      document.body.style.overflow = prev;
+    };
+  }, [onClose]);
+  return (
+    <div
+      className="fixed inset-0 z-[60] grid place-items-center bg-black/80 backdrop-blur-sm p-4 sm:p-8"
+      onClick={onClose}
+      role="dialog"
+      aria-modal="true"
+      aria-label={label}
+    >
+      <button
+        type="button"
+        onClick={onClose}
+        aria-label="Close"
+        className="absolute top-4 right-4 p-2 rounded-full glass-card glass-hover text-fg"
+      >
+        <X className="w-5 h-5" />
+      </button>
+      <figure
+        className="flex max-h-full max-w-full flex-col items-center gap-3"
+        onClick={(e) => e.stopPropagation()}
+      >
         <img
           src={src}
           alt={label}
-          loading="lazy"
-          onError={() => setFailed(true)}
-          className="w-full h-full object-cover object-top"
+          className="max-h-[82vh] max-w-[92vw] w-auto h-auto rounded-xl border border-border object-contain shadow-2xl"
         />
-      )}
+        <figcaption className="text-sm text-muted">{label}</figcaption>
+      </figure>
     </div>
   );
 }
 
 function AuthCard() {
   const { t } = useTranslation();
-  const params = new URLSearchParams(window.location.search);
+  // Snapshot the redirect params ONCE so we can clean them from the address bar below without
+  // dismissing the banners/reset-mode they drive (those read this stable snapshot, not the URL).
+  const [params] = useState(() => new URLSearchParams(window.location.search));
   const resetToken = params.get("reset");
   const bounced = params.get("access"); // Google denied → "requested" | "denied"
   const verify = params.get("verify"); // "ok" | "invalid"
+  const login = params.get("login"); // Google login blocked → "suspended"
+  const deleted = params.get("deleted"); // self-service account deletion just completed
+
+  // Strip the query string so the address bar stays clean (http://host/) after we've captured it.
+  useEffect(() => {
+    if (window.location.search) {
+      window.history.replaceState(null, "", window.location.pathname);
+    }
+  }, []);
 
   const [mode, setMode] = useState<Mode>(resetToken ? "reset" : "signin");
   const [email, setEmail] = useState("");
@@ -230,6 +333,8 @@ function AuthCard() {
       {verify === "invalid" && <Banner tone="warn">{t("welcome.auth.verifyInvalid")}</Banner>}
       {bounced === "requested" && <Banner tone="ok">{t("welcome.auth.accessRequested")}</Banner>}
       {bounced === "denied" && <Banner tone="warn">{t("welcome.auth.accessDenied")}</Banner>}
+      {login === "suspended" && <Banner tone="warn">{t("welcome.auth.suspended")}</Banner>}
+      {deleted && <Banner tone="ok">{t("welcome.auth.deleted")}</Banner>}
 
       {done ? (
         <div className="mt-3">

frontend/src/i18n/locales/de/welcome.json

@@ -68,6 +68,8 @@
     "verifyOk": "E-Mail bestätigt. Sobald ein Admin dein Konto freigibt, kannst du dich anmelden.",
     "verifyInvalid": "Dieser Bestätigungslink ist ungültig oder abgelaufen.",
     "accessRequested": "Danke — wir haben deine Anfrage erfasst. Ein Admin wird sie prüfen.",
-    "accessDenied": "Dieses Konto ist für diese Instanz noch nicht freigegeben — registriere dich unten oder bitte den Admin um Zugang."
+    "accessDenied": "Dieses Konto ist für diese Instanz noch nicht freigegeben — registriere dich unten oder bitte den Admin um Zugang.",
+    "suspended": "Dieses Konto wurde gesperrt und kann sich nicht anmelden. Falls das ein Irrtum ist, wende dich an den Betreiber (Details in deiner E-Mail).",
+    "deleted": "Dein Konto und alle Daten wurden endgültig gelöscht. Eine Bestätigung haben wir dir per E-Mail geschickt."
   }
 }

frontend/src/i18n/locales/en/welcome.json

@@ -68,6 +68,8 @@
     "verifyOk": "Email confirmed. Once an admin approves your account, you can sign in.",
     "verifyInvalid": "That verification link is invalid or has expired.",
     "accessRequested": "Thanks — we recorded your request. An admin will review it.",
-    "accessDenied": "That account isn't approved for this instance yet — register below or ask the admin for access."
+    "accessDenied": "That account isn't approved for this instance yet — register below or ask the admin for access.",
+    "suspended": "This account has been suspended and can't sign in. If you think this is a mistake, contact the operator (check your email for details).",
+    "deleted": "Your account and all its data were permanently deleted. We've emailed you a confirmation."
   }
 }

frontend/src/i18n/locales/hu/welcome.json

@@ -68,6 +68,8 @@
     "verifyOk": "E-mail megerősítve. Amint egy admin jóváhagyja a fiókodat, beléphetsz.",
     "verifyInvalid": "Ez a megerősítő link érvénytelen vagy lejárt.",
     "accessRequested": "Köszönjük — rögzítettük a kérésed. Egy admin felülvizsgálja.",
-    "accessDenied": "Ez a fiók még nincs jóváhagyva ehhez a példányhoz — regisztrálj lent, vagy kérj hozzáférést az admintól."
+    "accessDenied": "Ez a fiók még nincs jóváhagyva ehhez a példányhoz — regisztrálj lent, vagy kérj hozzáférést az admintól.",
+    "suspended": "Ez a fiók fel van függesztve, nem tud belépni. Ha tévedésnek gondolod, keresd az üzemeltetőt (a részletek az e-mailedben).",
+    "deleted": "A fiókod és minden adata véglegesen törölve lett. A megerősítést e-mailben is elküldtük."
   }
 }