feat(web): extend ArtistRef/AlbumRef + add HomePayload + new query keys

Adds sort_name/cover_url to ArtistRef, sort_title to AlbumRef (matching
backend Task 5 wire shape), HomePayload type, and qk.home/albumsAlpha/
artistTracks query keys. Updates existing test fixtures to satisfy the
new required fields.

Verified clean via 'npm run check' (0 errors, only pre-existing warnings).

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

web/src/routes/search/albums/albums.test.ts

@@ -44,7 +44,7 @@ function page<T>(items: T[], total: number, offset = 0, limit = 50): Page<T> {
 }
 
 const album: AlbumRef = {
-  id: 'al1', title: 'Kind of Blue', artist_id: 'a1', artist_name: 'Miles Davis',
+  id: 'al1', title: 'Kind of Blue', sort_title: 'Kind of Blue', artist_id: 'a1', artist_name: 'Miles Davis',
   year: 1959, track_count: 5, duration_sec: 2630, cover_url: '/api/albums/al1/cover'
 };