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/library.ts

@@ -201,6 +201,18 @@ export const libraryApi = api.injectEndpoints({
       }),
       invalidatesTags: (_r, _e, trackId) => [{ type: 'Track', id: trackId }],
     }),
+    // Enqueue a transcode to a cached Opus + HLS rendition (§6.6). Fire-and-
+    // forget: the worker does the work, playback keeps using the original.
+    optimizeTrack: build.mutation<
+      { status: string; job_id: string; quality: string },
+      { trackId: string; quality?: string }
+    >({
+      query: ({ trackId, quality = 'high' }) => ({
+        url: `/tracks/${trackId}/optimize`,
+        method: 'POST',
+        params: { quality },
+      }),
+    }),
   }),
   overrideExisting: false,
 });
@@ -219,4 +231,5 @@ export const {
   useLazyGetMetadataMatchesQuery,
   useApplyMetadataMutation,
   useEnrichTrackMutation,
+  useOptimizeTrackMutation,
 } = libraryApi;

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 {