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/albums/[id]/album.test.ts

@@ -56,7 +56,7 @@ afterEach(() => {
 describe('album detail page', () => {
   test('renders hero metadata + one TrackRow per track', () => {
     const detail: AlbumDetail = {
-      id: 'xyz', title: 'Kind of Blue',
+      id: 'xyz', title: 'Kind of Blue', sort_title: 'Kind of Blue',
       artist_id: 'md', artist_name: 'Miles Davis',
       year: 1959, track_count: 2, duration_sec: 544 + 565,
       cover_url: '/api/albums/xyz/cover',
@@ -83,7 +83,7 @@ describe('album detail page', () => {
 
   test('back link points to /artists/:artistId with the artist name', () => {
     const detail: AlbumDetail = {
-      id: 'xyz', title: 'T',
+      id: 'xyz', title: 'T', sort_title: 'T',
       artist_id: 'md', artist_name: 'Miles Davis',
       track_count: 0, duration_sec: 0,
       cover_url: '/api/albums/xyz/cover',