refactor(playback): move genreBrowsePlayback into the feature; utils/library now feature-free

genreBrowsePlayback is a "play X" queue builder -- it turns a genre seed into a
Track[] for the player, the genre analogue of playArtistShuffled which already
lives in features/playback/utils/playback. Consumed only by the 3 genre pages,
by no utils/library sibling, so the whole-file move is clean (no split). Its
Track/songToTrack edges become intra-feature; its remaining utils/library
siblings (advancedSearchLocal, albumBrowseSort, genreCatalogCountsCache,
genreAlbumBrowse, libraryReady) are plain infra deps.

utils/library now has ZERO @/features importers (source AND tests) -- the bulk
is ready to relocate to lib/library. tsc 0, lint 0, genre suite green.

src/features/playback/utils/playback/genreBrowsePlayback.test.ts

@@ -22,23 +22,23 @@ vi.mock('@/lib/api/subsonicClient', () => ({
   libraryScopeForServer: vi.fn(() => 'music'),
 }));
 
-vi.mock('./libraryReady', () => ({
+vi.mock('@/utils/library/libraryReady', () => ({
   libraryIsReady: vi.fn(),
 }));
 
 // Spread the real leaf module so other consumers pulled in transitively (the
 // album barrel reaches this via the artist↔album edge → useGenreAlbumBrowse needs
 // GENRE_ALBUM_FIRST_PAGE); only fetchGenreAlbumTotal is stubbed here.
-vi.mock('./genreAlbumBrowse', async (importOriginal) => ({
-  ...(await importOriginal<typeof import('./genreAlbumBrowse')>()),
+vi.mock('@/utils/library/genreAlbumBrowse', async (importOriginal) => ({
+  ...(await importOriginal<typeof import('@/utils/library/genreAlbumBrowse')>()),
   fetchGenreAlbumTotal: vi.fn(),
 }));
 
 import { libraryAdvancedSearch, libraryGetGenreAlbumCounts } from '@/lib/api/library';
 import { fetchAllSongsByGenre, getGenres } from '@/lib/api/subsonicGenres';
-import { fetchGenreAlbumTotal } from './genreAlbumBrowse';
-import { resetGenreCatalogCountsCacheForTests } from './genreCatalogCountsCache';
-import { libraryIsReady } from './libraryReady';
+import { fetchGenreAlbumTotal } from '@/utils/library/genreAlbumBrowse';
+import { resetGenreCatalogCountsCacheForTests } from '@/utils/library/genreCatalogCountsCache';
+import { libraryIsReady } from '@/utils/library/libraryReady';
 
 describe('genreBrowsePlayback', () => {
   beforeEach(() => {

src/features/playback/utils/playback/genreBrowsePlayback.ts

@@ -8,8 +8,8 @@ import { libraryScopeForServer } from '@/lib/api/subsonicClient';
 import type { Track } from '@/features/playback/store/playerStoreTypes';
 import { songToTrack } from '@/features/playback/utils/playback/songToTrack';
 import { shuffleArray } from '@/lib/util/shuffleArray';
-import { trackToSong } from './advancedSearchLocal';
-import { type AlbumBrowseSort } from './albumBrowseSort';
+import { trackToSong } from '@/utils/library/advancedSearchLocal';
+import { type AlbumBrowseSort } from '@/utils/library/albumBrowseSort';
 import {
   genreCatalogCacheKey,
   getInflightGenreCatalog,
@@ -17,9 +17,9 @@ import {
   peekGenreCatalogCache,
   trackInflightGenreCatalog,
   writeGenreCatalogCache,
-} from './genreCatalogCountsCache';
-import { fetchGenreAlbumTotal } from './genreAlbumBrowse';
-import { libraryIsReady } from './libraryReady';
+} from '@/utils/library/genreCatalogCountsCache';
+import { fetchGenreAlbumTotal } from '@/utils/library/genreAlbumBrowse';
+import { libraryIsReady } from '@/utils/library/libraryReady';
 
 /** Drop genres with no indexed albums/tracks (stale server list or orphan rows). */
 export function filterGenresWithContent(genres: SubsonicGenre[]): SubsonicGenre[] {

src/pages/GenreDetail.tsx

@@ -22,7 +22,7 @@ import { usePlayerStore } from '@/features/playback/store/playerStore';
 import {
   fetchGenreAlbumCount,
   fetchGenreTracksForPlayback,
-} from '../utils/library/genreBrowsePlayback';
+} from '@/features/playback/utils/playback/genreBrowsePlayback';
 import { lookupGenreAlbumCount } from '../utils/library/genreCatalogCountsCache';
 import { libraryScopeForServer } from '@/lib/api/subsonicClient';
 import {

src/pages/Genres.tsx

@@ -7,7 +7,7 @@ import { APP_MAIN_SCROLL_VIEWPORT_ID } from '../constants/appScroll';
 import { subscribeLibrarySyncIdle } from '@/lib/api/library';
 import { useAuthStore } from '../store/authStore';
 import { useLibraryIndexStore } from '../store/libraryIndexStore';
-import { fetchGenreCatalog, filterGenresWithContent } from '../utils/library/genreBrowsePlayback';
+import { fetchGenreCatalog, filterGenresWithContent } from '@/features/playback/utils/playback/genreBrowsePlayback';
 import { libraryScopeForServer } from '@/lib/api/subsonicClient';
 import { peekGenreCatalogCache } from '../utils/library/genreCatalogCountsCache';
 import { resolveIndexKey } from '../utils/server/serverIndexKey';

src/pages/RandomMix.tsx

@@ -13,7 +13,7 @@ import {
   fetchRandomMixSongsUntilFull,
   getMixMinRatingsConfigFromAuth,
 } from '../utils/mix/mixRatingFilter';
-import { fetchGenreCatalog } from '../utils/library/genreBrowsePlayback';
+import { fetchGenreCatalog } from '@/features/playback/utils/playback/genreBrowsePlayback';
 import { AUDIOBOOK_GENRES, filterRandomMixSongs } from '../utils/componentHelpers/randomMixHelpers';
 import RandomMixHeader from '../components/randomMix/RandomMixHeader';
 import RandomMixFiltersPanel from '../components/randomMix/RandomMixFiltersPanel';