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/lib/api/queries.test.ts

@@ -30,3 +30,11 @@ describe('qk search keys', () => {
     expect(qk.searchTracks('foo')).toEqual(['searchTracks', { q: 'foo' }]);
   });
 });
+
+describe('qk M6a keys', () => {
+  test('M6a query keys are stable', () => {
+    expect(qk.home()).toEqual(['home']);
+    expect(qk.albumsAlpha()).toEqual(['albumsAlpha']);
+    expect(qk.artistTracks('a1')).toEqual(['artistTracks', 'a1']);
+  });
+});

web/src/lib/api/queries.ts

@@ -34,6 +34,9 @@ export const qk = {
     ['adminQuarantineActions', { limit: limit ?? 50 }] as const,
   suggestions:            (limit?: number) =>
     ['suggestions', { limit: limit ?? 12 }] as const,
+  home:         ()                 => ['home'] as const,
+  albumsAlpha:  ()                 => ['albumsAlpha'] as const,
+  artistTracks: (artistId: string) => ['artistTracks', artistId] as const,
 };
 
 export function createArtistsQuery(sort: ArtistSort) {

web/src/lib/api/types.ts

@@ -12,12 +12,15 @@ export type Page<T> = {
 export type ArtistRef = {
   id: string;
   name: string;
+  sort_name: string;
   album_count: number;
+  cover_url: string;   // "" when no representative album cover
 };
 
 export type AlbumRef = {
   id: string;
   title: string;
+  sort_title: string;
   artist_id: string;
   artist_name: string;
   year?: number;
@@ -236,3 +239,13 @@ export type ArtistSuggestion = {
   score: number;
   attribution: SeedContribution[]; // up to 3 entries, ordered by contribution DESC
 };
+
+// Mirrors internal/api/types.go HomePayload. All slices are non-null
+// per the server contract — empty sections render as [].
+export type HomePayload = {
+  recently_added_albums: AlbumRef[];
+  rediscover_albums:     AlbumRef[];
+  rediscover_artists:    ArtistRef[];
+  most_played_tracks:    TrackRef[];
+  last_played_artists:   ArtistRef[];
+};