feat(playlists): Sync to YouTube UI + delete-on-YouTube choice

Editable local playlists get an Export/Sync to YouTube button (write-scope gated):
it fetches a dry-run plan, shows a confirm with the change counts, quota estimate
and divergence warning, then pushes. An 'unsynced changes' badge and an accented
YouTube icon mark linked playlists with local edits. Deleting a linked playlist
offers 'delete on YouTube too' vs 'here only'. Trilingual strings (HU/EN/DE).

frontend/src/App.tsx

@@ -232,7 +232,7 @@ export default function App() {
           ) : page === "stats" && meQuery.data!.role === "admin" ? (
             <Stats />
           ) : page === "playlists" ? (
-            <Playlists />
+            <Playlists canWrite={meQuery.data!.can_write} />
           ) : (
             <Feed
               filters={filters}