fix(imageCache): give every cached <img> its own object URL

The previous design kept a single global Map<cacheKey, objectURL> with an
LRU cap of 150 and aggressively revoked the oldest URL on overflow. On
libraries with more than 150 cached covers (artist + album grids quickly
exceed that), an in-use URL would get revoked because a different
consumer pushed it out of the cache, producing the "Failed to load
resource: blob:..." flood that several users have reported.

Refactor the cache to be blob-centric:

- Public API is now getCachedBlob() returning the Blob itself.
- In-memory LRU now holds Blobs (cap 200), not URLs. Map-entry eviction
  drops the strong reference and lets the GC free the Blob once no
  consumer (object URL, <img>, <canvas>) still holds it. No revoke choreography needed.
- useCachedUrl creates its own URL.createObjectURL on blob arrival and
  revokes it on cleanup with a 500 ms grace delay so the DOM <img> has
  time to finish decoding the URL we just took away.
- All existing callers keep their string-returning API; no call-site
  changes outside the hook itself.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/FullscreenPlayer.tsx

@@ -7,7 +7,7 @@ import {
 import { usePlayerStore } from '../store/playerStore';
 import { buildCoverArtUrl, coverArtCacheKey, getArtistInfo, star, unstar } from '../api/subsonic';
 import { useCachedUrl } from './CachedImage';
-import { getCachedUrl } from '../utils/imageCache';
+import { getCachedBlob } from '../utils/imageCache';
 import { extractCoverColors } from '../utils/dynamicColors';
 import { useTranslation } from 'react-i18next';
 import { useLyrics, type WordLyricsLine } from '../hooks/useLyrics';
@@ -740,7 +740,7 @@ export default function FullscreenPlayer({ onClose }: FullscreenPlayerProps) {
     if (!nextCoverArt) return;
     const url = buildCoverArtUrl(nextCoverArt, 300);
     const key = coverArtCacheKey(nextCoverArt, 300);
-    getCachedUrl(url, key).catch(() => {});
+    getCachedBlob(url, key).catch(() => {});
   }, [nextCoverArt]);
 
   // Lyrics settings popover state