feat(account): GDPR self-service account + data deletion (5d)

Add DELETE /api/me/account: permanently erases the signed-in account and all its
personal data — OAuth tokens, subscriptions, tags, video states, playlists,
notifications all cascade on the users row (FK ON DELETE CASCADE); quota-audit
events are kept but anonymised (SET NULL); the email's invite/whitelist row is
removed too. Guards: the shared demo account can't be deleted, and the last
remaining admin can't delete itself. Frontend: a Danger zone in Settings -> Account
(non-demo) with a danger-confirm; on success the session clears and the app lands
on the welcome page. EN/HU/DE. Verified via curl: self-delete + session clear +
demo 403.

frontend/src/components/SettingsPanel.tsx

@@ -1,11 +1,12 @@
 import { useState } from "react";
 import { useTranslation } from "react-i18next";
-import { Bell, Check, Monitor, RotateCcw, Save, User } from "lucide-react";
+import { Bell, Check, Monitor, RotateCcw, Save, Trash2, User } from "lucide-react";
 import { SCHEMES, type Scheme, type ThemePrefs } from "../lib/theme";
-import { type Me } from "../lib/api";
+import { api, type Me } from "../lib/api";
 import Avatar from "./Avatar";
 import { notify, type NotifSettings } from "../lib/notifications";
 import Tooltip from "./Tooltip";
+import { useConfirm } from "./ConfirmProvider";
 
 // The Settings page edits server-persisted preferences as a draft: changes apply locally
 // for instant preview but reach the server only on an explicit Save (or revert on Discard).
@@ -354,6 +355,22 @@ function AccessRow({
 
 function Account({ me, onOpenWizard }: { me: Me; onOpenWizard: () => void }) {
   const { t } = useTranslation();
+  const confirm = useConfirm();
+  const onDeleteAccount = async () => {
+    const ok = await confirm({
+      title: t("settings.account.deleteTitle"),
+      message: t("settings.account.deleteConfirm"),
+      confirmLabel: t("settings.account.deleteConfirmButton"),
+      danger: true,
+    });
+    if (!ok) return;
+    try {
+      await api.deleteAccount();
+      window.location.reload(); // session cleared server-side → lands on the welcome page
+    } catch {
+      /* the global error dialog surfaces the reason (e.g. last admin) */
+    }
+  };
   return (
     <>
     <Section title={t("settings.account.title")}>
@@ -410,6 +427,19 @@ function Account({ me, onOpenWizard }: { me: Me; onOpenWizard: () => void }) {
         </button>
       </Section>
     )}
+
+    {!me.is_demo && (
+      <Section title={t("settings.account.dangerZone")}>
+        <p className="text-xs text-muted leading-relaxed mb-2">{t("settings.account.deleteHint")}</p>
+        <button
+          onClick={onDeleteAccount}
+          className="inline-flex items-center gap-1.5 px-3 py-2 rounded-xl text-sm border border-red-500/40 text-red-400 hover:bg-red-500/10 transition"
+        >
+          <Trash2 className="w-4 h-4" />
+          {t("settings.account.deleteAccount")}
+        </button>
+      </Section>
+    )}
     </>
   );
 }

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

@@ -55,6 +55,12 @@
     "enable": "Aktivieren",
     "enableHint": "Leitet zu Google weiter, um die Berechtigung zu erteilen. Google zeigt einen Hinweis „nicht verifizierte App“ — das ist zu erwarten; klicke auf Erweitert → Weiter zu Siftlode.",
     "walkMeThrough": "Führe mich durch die Einrichtung",
+    "dangerZone": "Gefahrenzone",
+    "deleteHint": "Löscht dein Konto und alle deine Daten dauerhaft — Abos, Tags, Wiedergabeverlauf, Playlists und Einstellungen. Kann nicht rückgängig gemacht werden.",
+    "deleteAccount": "Mein Konto löschen",
+    "deleteTitle": "Konto löschen?",
+    "deleteConfirm": "Dies löscht dein Konto und alle deine Daten (Abos, Tags, angesehen/gespeichert/ausgeblendet, Playlists, Einstellungen) dauerhaft. Es kann nicht rückgängig gemacht werden.",
+    "deleteConfirmButton": "Alles löschen",
     "demoNotice": "Dies ist das gemeinsame Demo-Konto. Es hat keine YouTube-Verbindung — du kannst die gesamte gemeinsame Bibliothek durchsuchen, filtern und sortieren, Playlists erstellen und Dinge ausprobieren, aber nichts berührt ein echtes YouTube-Konto."
   },
   "demo": {

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

@@ -55,6 +55,12 @@
     "enable": "Enable",
     "enableHint": "Redirects to Google to grant the permission. Google shows an 'unverified app' notice — that's expected; click Advanced → Go to Siftlode.",
     "walkMeThrough": "Walk me through setup",
+    "dangerZone": "Danger zone",
+    "deleteHint": "Permanently delete your account and all your data — subscriptions, tags, watch history, playlists and settings. This can't be undone.",
+    "deleteAccount": "Delete my account",
+    "deleteTitle": "Delete your account?",
+    "deleteConfirm": "This permanently erases your account and all your data (subscriptions, tags, watch/saved/hidden state, playlists, settings). It can't be undone.",
+    "deleteConfirmButton": "Delete everything",
     "demoNotice": "This is the shared demo account. It has no YouTube connection — you can browse the whole shared library, filter and sort it, build playlists and try things out, but nothing touches a real YouTube account."
   },
   "demo": {

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

@@ -55,6 +55,12 @@
     "enable": "Engedélyezés",
     "enableHint": "Átirányít a Google-höz az engedély megadásához. A Google „nem ellenőrzött alkalmazás” figyelmeztetést mutat — ez normális; kattints a Speciális → Tovább a Siftlode-ra lehetőségre.",
     "walkMeThrough": "Vezess végig a beállításon",
+    "dangerZone": "Veszélyzóna",
+    "deleteHint": "Véglegesen törli a fiókodat és minden adatodat — feliratkozások, címkék, megtekintési előzmény, lejátszási listák és beállítások. Nem vonható vissza.",
+    "deleteAccount": "Fiókom törlése",
+    "deleteTitle": "Törlöd a fiókodat?",
+    "deleteConfirm": "Ez véglegesen törli a fiókodat és minden adatodat (feliratkozások, címkék, megnézett/mentett/elrejtett állapot, lejátszási listák, beállítások). Nem vonható vissza.",
+    "deleteConfirmButton": "Minden törlése",
     "demoNotice": "Ez a közös demo fiók. Nincs YouTube-kapcsolata — böngészheted a teljes közös könyvtárat, szűrheted és rendezheted, listákat építhetsz és kipróbálhatsz dolgokat, de semmi nem nyúl valódi YouTube-fiókhoz."
   },
   "demo": {

frontend/src/lib/api.ts

@@ -480,6 +480,8 @@ export interface AdminUserRow {
 export const api = {
   me: (): Promise<Me> => req("/api/me"),
   accounts: (): Promise<Account[]> => req("/api/me/accounts"),
+  deleteAccount: (): Promise<{ deleted: boolean }> =>
+    req("/api/me/account", { method: "DELETE" }),
   switchAccount: (userId: number): Promise<{ ok: boolean; user_id: number }> =>
     req("/api/me/switch", { method: "POST", body: JSON.stringify({ user_id: userId }) }),
   version: (): Promise<VersionInfo> => req("/api/version"),