feat(player): stream at the chosen quality + per-track optimize (§6.6)

The Playback quality setting now drives streaming: getStreamUrl appends
?quality= and useAudioPlayer feeds the server-synced streamQuality, so the
backend transcodes on demand (miss → original). Adds an optimizeTrack mutation
and an Optimize action in the metadata editor to warm a track's rendition.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/api/endpoints/streaming.ts

@@ -5,9 +5,17 @@ import { getApiBaseUrl } from '../../config/runtime-config';
  * param because `<audio>` can't send an `Authorization` header; the backend
  * accepts `?token=` on `GET /stream/{id}` for exactly this reason.
  */
-export function getStreamUrl(trackId: string, token: string): string {
+export function getStreamUrl(
+  trackId: string,
+  token: string,
+  quality?: string,
+): string {
   const base = getApiBaseUrl();
-  return `${base}/stream/${trackId}?token=${encodeURIComponent(token)}`;
+  const q =
+    quality && quality !== 'original'
+      ? `&quality=${encodeURIComponent(quality)}`
+      : '';
+  return `${base}/stream/${trackId}?token=${encodeURIComponent(token)}${q}`;
 }
 
 export function getCoverUrl(artUrl: string | undefined): string | undefined {