feat(playlists): reset a playlist to its YouTube state (discard local edits)

The in-session undo/redo is lost when switching playlists, leaving no way to undo
local edits to a YouTube-linked list afterwards. Add a per-playlist 'Reset to YouTube'
action (shown when a linked playlist is dirty) that force-repulls that single playlist
from YouTube, replacing its items/order/name and clearing dirty — even though the bulk
read-sync skips dirty playlists. Backend: repull_playlist() + POST /api/playlists/
{id}/revert-youtube (read-scope gated). Confirm dialog (destructive). Trilingual.

frontend/src/components/Playlists.tsx

@@ -27,6 +27,7 @@ import {
   Play,
   Plus,
   RefreshCw,
+  RotateCcw,
   Trash2,
   Upload,
   X,
@@ -326,6 +327,28 @@ export default function Playlists({ canWrite }: { canWrite: boolean }) {
   const linked = editable && !!detail?.yt_playlist_id;
   const [syncing, setSyncing] = useState(false);
   const [pushing, setPushing] = useState(false);
+  const [reverting, setReverting] = useState(false);
+
+  async function revertToYoutube() {
+    if (selectedId == null || !detail || reverting) return;
+    const ok = await confirm({
+      title: t("playlists.revertTitle"),
+      message: t("playlists.revertMsg"),
+      confirmLabel: t("playlists.revertConfirm"),
+      danger: true,
+    });
+    if (!ok) return;
+    setReverting(true);
+    try {
+      await api.revertPlaylist(selectedId);
+      refreshAll();
+      notify({ level: "success", message: t("playlists.revertDone") });
+    } catch {
+      notify({ level: "warning", message: t("playlists.revertFailed") });
+    } finally {
+      setReverting(false);
+    }
+  }
 
   async function pushToYoutube() {
     if (selectedId == null || !detail || pushing) return;
@@ -685,9 +708,20 @@ export default function Playlists({ canWrite }: { canWrite: boolean }) {
                     </button>
                   )}
                   {linked && detail.dirty && (
-                    <span className="inline-flex items-center gap-1.5 text-[11px] px-2.5 py-1.5 rounded-lg text-accent">
-                      {t("playlists.unsynced")}
-                    </span>
+                    <>
+                      <button
+                        onClick={revertToYoutube}
+                        disabled={reverting}
+                        title={t("playlists.revert")}
+                        className="inline-flex items-center gap-1.5 text-xs px-3 py-1.5 rounded-lg border border-border text-muted hover:text-fg hover:border-accent transition disabled:opacity-40"
+                      >
+                        <RotateCcw className={`w-3.5 h-3.5 ${reverting ? "animate-spin" : ""}`} />
+                        {t("playlists.revert")}
+                      </button>
+                      <span className="inline-flex items-center gap-1.5 text-[11px] px-2.5 py-1.5 rounded-lg text-accent">
+                        {t("playlists.unsynced")}
+                      </span>
+                    </>
                   )}
                   {mirrored && (
                     <span className="inline-flex items-center gap-1.5 text-[11px] px-2.5 py-1.5 rounded-lg text-muted">

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

@@ -20,6 +20,12 @@
   "exportToYoutube": "Zu YouTube exportieren",
   "pushToYoutube": "Mit YouTube synchronisieren",
   "unsynced": "Nicht synchronisierte Änderungen",
+  "revert": "Von YouTube zurücksetzen",
+  "revertTitle": "Lokale Änderungen verwerfen?",
+  "revertMsg": "Dies lädt die Wiedergabeliste von YouTube neu und verwirft deine nicht synchronisierten lokalen Änderungen (Reihenfolge, Hinzufügungen, Entfernungen, Umbenennung). Fortfahren?",
+  "revertConfirm": "Verwerfen & neu laden",
+  "revertDone": "Von YouTube neu geladen ✓",
+  "revertFailed": "Neuladen von YouTube fehlgeschlagen.",
   "pushTitle": "Mit YouTube synchronisieren",
   "pushConfirm": "Synchronisieren",
   "pushPlanCreate": "Eine neue YouTube-Wiedergabeliste mit {{count}} Videos erstellen? (~{{units}} Kontingenteinheiten; heute noch {{left}} übrig.)",

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

@@ -20,6 +20,12 @@
   "exportToYoutube": "Export to YouTube",
   "pushToYoutube": "Sync to YouTube",
   "unsynced": "Unsynced changes",
+  "revert": "Reset to YouTube",
+  "revertTitle": "Discard local changes?",
+  "revertMsg": "This reloads the playlist from YouTube and discards your unsynced local changes (order, additions, removals, rename). Continue?",
+  "revertConfirm": "Discard & reload",
+  "revertDone": "Reloaded from YouTube ✓",
+  "revertFailed": "Couldn't reload from YouTube.",
   "pushTitle": "Sync to YouTube",
   "pushConfirm": "Sync",
   "pushPlanCreate": "Create a new YouTube playlist with {{count}} videos? (~{{units}} quota units; {{left}} left today.)",

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

@@ -20,6 +20,12 @@
   "exportToYoutube": "Exportálás YouTube-ra",
   "pushToYoutube": "Szinkron YouTube-ra",
   "unsynced": "Nem szinkronizált változások",
+  "revert": "Visszaállítás YouTube-ról",
+  "revertTitle": "Eldobod a helyi módosításokat?",
+  "revertMsg": "Ez újratölti a listát a YouTube-ról, és eldobja a nem szinkronizált helyi módosításaidat (sorrend, hozzáadás, eltávolítás, átnevezés). Folytatod?",
+  "revertConfirm": "Eldobás és újratöltés",
+  "revertDone": "Újratöltve a YouTube-ról ✓",
+  "revertFailed": "Nem sikerült újratölteni a YouTube-ról.",
   "pushTitle": "Szinkron YouTube-ra",
   "pushConfirm": "Szinkron",
   "pushPlanCreate": "Létrehozol egy új YouTube-listát {{count}} videóval? (~{{units}} kvótaegység; ma még {{left}} maradt.)",

frontend/src/lib/api.ts

@@ -370,6 +370,8 @@ export const api = {
     req(`/api/playlists/watch-later/${videoId}`, { method: "DELETE" }),
   syncYoutubePlaylists: (): Promise<{ synced: number; reason?: string }> =>
     req("/api/playlists/sync-youtube", { method: "POST" }),
+  revertPlaylist: (id: number): Promise<{ items: number }> =>
+    req(`/api/playlists/${id}/revert-youtube`, { method: "POST" }),
   playlistPushPlan: (id: number): Promise<PushPlan> =>
     req(`/api/playlists/${id}/push-plan`),
   pushPlaylist: (id: number): Promise<PushResult> =>