Fix 8 code-review findings across transcode queue, requests, cleanup, music

- Episode transcode (single + bulk) now accepts storage_type=scan, matching
  stream_episode and the movie-transcode endpoint — Library-Scan-imported
  TV episodes can finally be transcoded, not just streamed.
- retry_job now forwards content_type, fixing retry for failed/cancelled
  episode jobs (was silently treating them as movies and failing again).
- cancel_job now updates the correct collection (movies vs episodes) based
  on content_type instead of always writing to db.movies.
- approve_request atomically claims the request (pending -> approving)
  before contacting Radarr/Sonarr, so a double-click or two concurrent
  admins can't both add the same content; releases the claim back to
  pending on any failure so a fixable error can be retried.
- Music enrichment's update_many now re-checks album_art_url is still
  empty, so it no longer clobbers art an admin manually set via PATCH.
- Library Cleanup's dangling-refs scan now also checks episode_progress
  for rows referencing a deleted episode (previously only watchlist/
  progress against movie_id were checked).
- Settings now surfaces a failed bulk-TMDB-enrich run as an error instead
  of a false "Enrichment done" success summary.
- Music player's isPlaying now syncs from the audio element's native
  play/pause events instead of only being set inside togglePlay/track-
  change, so it can't drift from actual playback state (buffering stalls,
  OS media-key pauses, etc).

frontend/src/pages/Settings.jsx

@@ -140,7 +140,11 @@ export default function Settings() {
       setEnrich(data);
       if (!data.running) {
         clearInterval(t);
-        toast.success(`Enrichment done — ${data.enriched} enriched, ${data.skipped} already complete, ${data.failed} not found`);
+        if (data.error) {
+          toast.error(`Enrichment failed: ${data.error}`);
+        } else {
+          toast.success(`Enrichment done — ${data.enriched} enriched, ${data.skipped} already complete, ${data.failed} not found`);
+        }
       }
     }, 2000);
     return () => clearInterval(t);
@@ -210,7 +214,12 @@ export default function Settings() {
                 <button type="button" onClick={enrichAll} disabled={enrich?.running} className="text-xs uppercase tracking-[0.2em] border border-[#222] hover:border-[#D9381E] hover:text-[#D9381E] text-[#8A8A8A] px-4 py-2 transition-colors disabled:opacity-50" data-testid="enrich-all-button">
                   {enrich?.running ? `Enriching… ${enrich.done}/${enrich.total}` : "Bulk enrich all movies →"}
                 </button>
-                {enrich && !enrich.running && enrich.total > 0 && (
+                {enrich && !enrich.running && enrich.error && (
+                  <span className="text-xs text-[#fca5a5]" data-testid="enrich-all-error">
+                    Last run failed: {enrich.error}
+                  </span>
+                )}
+                {enrich && !enrich.running && !enrich.error && enrich.total > 0 && (
                   <span className="text-xs text-[#8A8A8A]" data-testid="enrich-all-summary">
                     Last run: {enrich.enriched} enriched · {enrich.skipped} already complete · {enrich.failed} not found on TMDB
                   </span>