fix(home): Discover Songs covers for local-index tracks (#874)

* fix(home): pre-warm and prefetch Discover Songs row covers

The Discover Songs raблин. il came out of the cover pipeline merge with two
gaps that left its cards stuck on the placeholder disc icon on cold
caches.

- `warmHomeMainstageCovers` walked `heroAlbums` / `recent` / `random`
  through `ensureAlbumCoverMisses` + `predecodeWarmAlbums` but skipped
  `discoverSongs`, so songs that were peeked but missed on disk had to
  wait for lazy per-card ensure
- `Home.tsx`'s `coverPrefetchRegister` lumped `songRefs` into a
  `cappedRest` slice already saturated by 48 album refs + 16 artist
  refs at a 24-entry cap, so the song row's background prefetch was
  discarded entirely

Fix: ensure + decode-warm the Discover Songs cells alongside the album
rails, and register the song refs in their own bucket with a sane cap
and `middle` priority. Both follow the same shape as the working album
rails — no behavior change for surfaces that were already painting.

* fix(library): resolve track cover art from albumId for local index songs

Discover Songs uses runLocalRandomSongs; trackToSong only mapped coverArtId,
so rows with empty cover_art_id but a valid album_id showed the disc
placeholder. Mirror Rust COALESCE(cover_art_id, album_id) and Live Search's
coverArt ?? albumId in trackToSong, SongCard, and Home prefetch.

* docs(release): note Discover Songs cover fix in CHANGELOG and credits (PR #874)

* docs(release): credit PR #874 to Psychotoxical and cucadmuh jointly

* chore(credits): drop PR #874 from settingsCredits — minor fix

---------

Co-authored-by: Psychotoxical <171614930+Psychotoxical@users.noreply.github.com>

src/utils/library/advancedSearchLocal.test.ts

@@ -2,7 +2,12 @@ import { describe, it, expect, beforeEach } from 'vitest';
 import { onInvoke } from '@/test/mocks/tauri';
 import { useAuthStore } from '@/store/authStore';
 import { useLibraryIndexStore } from '@/store/libraryIndexStore';
-import { runLocalAdvancedSearch, runLocalSongBrowse, trackToSong } from './advancedSearchLocal';
+import {
+  resolveTrackCoverArtId,
+  runLocalAdvancedSearch,
+  runLocalSongBrowse,
+  trackToSong,
+} from './advancedSearchLocal';
 
 const opts = (over: Partial<Parameters<typeof runLocalAdvancedSearch>[1]> = {}) => ({
   query: '',
@@ -100,6 +105,30 @@ describe('runLocalAdvancedSearch', () => {
     });
   });
 
+  it('resolveTrackCoverArtId falls back to albumId when coverArtId is empty', () => {
+    expect(
+      resolveTrackCoverArtId(
+        { coverArtId: undefined, albumId: 'al-42' },
+        { coverArt: '', albumId: 'al-42' },
+      ),
+    ).toBe('al-42');
+    expect(resolveTrackCoverArtId({ coverArtId: 'cv1', albumId: 'al-42' })).toBe('cv1');
+  });
+
+  it('trackToSong sets coverArt from albumId when the index row has no cover_art_id', () => {
+    const song = trackToSong({
+      serverId: 's1',
+      id: 't1',
+      title: 'T',
+      album: 'Alb',
+      albumId: 'al-42',
+      durationSec: 100,
+      syncedAt: 0,
+      rawJson: { id: 't1', title: 'T', artist: 'A', album: 'Alb', albumId: 'al-42', duration: 100 },
+    });
+    expect(song.coverArt).toBe('al-42');
+  });
+
   it('trackToSong keeps resolved bpm and source over rawJson tag', () => {
     const song = trackToSong({
       serverId: 's1',