fix(demo): graceful UX when YouTube actions are unavailable

The shared demo account no longer hits YouTube affordances: the onboarding
wizard never opens (or renders) for it, the empty-feed prompt nudges into
the shared library instead of the connect wizard, and the browser-facing
/auth/upgrade redirects the demo home instead of returning a raw 403 JSON.

backend/app/auth.py

@@ -320,13 +320,17 @@ def require_human(user: User = Depends(current_user)) -> User:
 
 @router.get("/upgrade")
 async def upgrade(
-    request: Request, access: str = "read", user: User = Depends(require_human)
+    request: Request, access: str = "read", user: User = Depends(current_user)
 ):
     """Incremental consent for the onboarding wizard. `access=read` grants YouTube
     read-only (enough to build the feed); `access=write` additionally grants management
     (unsubscribe). The shared callback stores whatever Google returns, so `can_read` /
     `can_write` flip on once granted. Anything other than an explicit `write` defaults to
     the least-privileged read scope."""
+    # This is the browser-facing redirect entry point, so the shared demo account is bounced
+    # straight home (no YouTube link is ever attached to it) rather than shown a raw 403.
+    if user.is_demo:
+        return RedirectResponse(url="/")
     scope = WRITE_SCOPES if access == "write" else READ_SCOPES
     return await oauth.google.authorize_redirect(
         request,

frontend/src/App.tsx

@@ -291,13 +291,14 @@ export default function App() {
               setFilters={setFilters}
               view={view}
               canRead={meQuery.data!.can_read}
+              isDemo={meQuery.data!.is_demo}
               onOpenWizard={() => setWizardOpen(true)}
             />
           )}
           </main>
         </div>
       </div>
-      {wizardOpen && meQuery.data && (
+      {wizardOpen && meQuery.data && !meQuery.data.is_demo && (
         <OnboardingWizard me={meQuery.data} onClose={() => setWizardOpen(false)} />
       )}
       {aboutOpen && (

frontend/src/components/Feed.tsx

@@ -68,12 +68,14 @@ export default function Feed({
   setFilters,
   view,
   canRead,
+  isDemo = false,
   onOpenWizard,
 }: {
   filters: FeedFilters;
   setFilters: (f: FeedFilters) => void;
   view: "grid" | "list";
   canRead: boolean;
+  isDemo?: boolean;
   onOpenWizard: () => void;
 }) {
   const { t } = useTranslation();
@@ -204,14 +206,28 @@ export default function Feed({
 
   if (query.isLoading) return <div className="p-8 text-muted">{t("feed.loading")}</div>;
   if (query.isError) return <div className="p-8 text-muted">{t("feed.loadError")}</div>;
-  // Onboarding empty state (no YouTube + own subscriptions): a dedicated full-page prompt,
-  // with no toolbar (content-type/sort would be meaningless here).
+  // Empty "my" feed with no YouTube access. The shared demo account can never connect
+  // YouTube, so it gets a gentle nudge into the shared library instead of the connect
+  // wizard; real users get the onboarding prompt. No toolbar (sort/type are meaningless).
   if (items.length === 0 && !canRead && filters.scope === "my")
     return (
         <div className="p-8 grid place-items-center text-center">
           <div className="max-w-sm">
-            <h2 className="text-lg font-semibold">{t("feed.emptyTitle")}</h2>
-            <p className="text-sm text-muted mt-2 mb-4">{t("feed.emptyBody")}</p>
+            <h2 className="text-lg font-semibold">
+              {isDemo ? t("feed.demoEmptyTitle") : t("feed.emptyTitle")}
+            </h2>
+            <p className="text-sm text-muted mt-2 mb-4">
+              {isDemo ? t("feed.demoEmptyBody") : t("feed.emptyBody")}
+            </p>
+            {isDemo ? (
+              <button
+                onClick={() => setFilters({ ...filters, scope: "all" })}
+                className="inline-flex items-center justify-center gap-2 px-5 py-2.5 rounded-xl font-semibold bg-accent text-accent-fg hover:opacity-90 transition"
+              >
+                {t("feed.browseLibrary")}
+              </button>
+            ) : (
+              <>
                 <button
                   onClick={onOpenWizard}
                   className="inline-flex items-center justify-center gap-2 px-5 py-2.5 rounded-xl font-semibold bg-accent text-accent-fg hover:opacity-90 transition"
@@ -224,6 +240,8 @@ export default function Feed({
                 >
                   {t("feed.browseShared")}
                 </button>
+              </>
+            )}
           </div>
         </div>
       );

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

@@ -5,6 +5,9 @@
   "emptyBody": "Verbinde dein YouTube-Konto, um deine Abos zu importieren und deinen Feed aufzubauen.",
   "setUp": "Meinen Feed einrichten",
   "browseShared": "Oder einfach die gemeinsame Bibliothek durchsuchen",
+  "demoEmptyTitle": "Hier in der Demo ist nichts",
+  "demoEmptyBody": "Das Demo-Konto hat keine eigenen Abos — aber die gesamte gemeinsame Bibliothek steht dir offen: durchsuchen, filtern und sortieren.",
+  "browseLibrary": "Bibliothek durchsuchen",
   "noMatches": "Keine Videos entsprechen diesen Filtern.",
   "videoCount_one": "{{formattedCount}} Video",
   "videoCount_other": "{{formattedCount}} Videos",

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

@@ -5,6 +5,9 @@
   "emptyBody": "Connect your YouTube account to import your subscriptions and build your feed.",
   "setUp": "Set up my feed",
   "browseShared": "Or just browse the shared library",
+  "demoEmptyTitle": "Nothing here in the demo",
+  "demoEmptyBody": "The demo account has no subscriptions of its own — but the whole shared library is yours to explore, filter and sort.",
+  "browseLibrary": "Browse the library",
   "noMatches": "No videos match these filters.",
   "videoCount_one": "{{formattedCount}} video",
   "videoCount_other": "{{formattedCount}} videos",

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

@@ -5,6 +5,9 @@
   "emptyBody": "Kösd össze a YouTube-fiókodat, hogy importáld a feliratkozásaidat, és felépítsd a hírfolyamodat.",
   "setUp": "Hírfolyam beállítása",
   "browseShared": "Vagy csak böngészd a közös könyvtárat",
+  "demoEmptyTitle": "Itt a demóban nincs semmi",
+  "demoEmptyBody": "A demo fióknak nincsenek saját feliratkozásai — de a teljes közös könyvtár a tiéd: böngészd, szűrd és rendezd kedvedre.",
+  "browseLibrary": "Könyvtár böngészése",
   "noMatches": "Egy videó sem felel meg ezeknek a szűrőknek.",
   "videoCount_one": "{{formattedCount}} videó",
   "videoCount_other": "{{formattedCount}} videó",