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']);
+  });
+});