refactor(playback): move the audio engine into features/playback

Relocate the playback/queue/transport/audio-output engine out of the type-first
store/ + utils/playback/ + utils/audio/ dirs into a cohesive src/features/playback/,
structure-preserving:
  store/<x>                    -> features/playback/store/<x>
  store/audioListenerSetup/<x> -> features/playback/store/audioListenerSetup/<x>
  utils/playback/<x>           -> features/playback/utils/playback/<x>
  utils/audio/<x>              -> features/playback/utils/audio/<x>

184 files moved (107 source + 77 tests), 365 consumers rewritten. Pure move — no
behavior change, no state-split (the playerStore state-split stays a separate M5
question). Enabled by this session's decouple seams (artist/offline/orbit/auth →
core registries), so the engine carries no inbound core->feature inversion: store/
now holds only the 50 cross-cutting global stores (auth family, the seams, library
index, UI/settings stores).

KEPT OUT of the move (would re-create global->engine edges): the 3 pure config
helpers utils/audio/{loudnessPreAnalysisSlider,hiResCrossfadeResample} +
utils/playback/autodjOverlapCap (authStore + settings UI read them — they stay in
utils/). Ambiguous view-state stores (eqStore, queueToolbarStore,
playerBarLayoutStore) stay global (no engine imports).

Consumers use DEEP paths (@/features/playback/...), no barrel — matches the lib/
approach and avoids barrel-mock-collapse across the 140 usePlayerStore consumers.
Two tolerated type-only core->feature edges remain (localPlaybackStore->QueueItemRef,
localPlaybackMigration->HotCacheEntry, both erased).

tsc 0, lint 0, full suite 319/2353 green, iron-rule clean (no runtime store->feature
import). Behavior-touching only via the prerequisite bridge seam (already QA-flagged);
the move itself is pure.

src/features/nowPlaying/components/NowPlayingDropdown.tsx

@@ -6,7 +6,7 @@ import { createPortal } from 'react-dom';
 import { PlayCircle, Pause, User, Radio, RefreshCw } from 'lucide-react';
 import { nowPlayingPresence } from '@/features/nowPlaying/api/nowPlayingPresence';
 import { useAuthStore } from '@/store/authStore';
-import { usePlayerStore } from '@/store/playerStore';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
 import { useTranslation } from 'react-i18next';
 import { useNavigate } from 'react-router-dom';
 

src/features/nowPlaying/components/NowPlayingInfo.tsx

@@ -5,13 +5,13 @@ import React, { useEffect, useLayoutEffect, useMemo, useRef, useState } from 're
 import { useTranslation } from 'react-i18next';
 import { Info } from 'lucide-react';
 import { open as shellOpen } from '@tauri-apps/plugin-shell';
-import { usePlayerStore } from '@/store/playerStore';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
 import { useAuthStore } from '@/store/authStore';
 import { usePlaybackServerId } from '@/hooks/usePlaybackServerId';
 import { fetchBandsintownEvents, type BandsintownEvent } from '@/api/bandsintown';
 import CachedImage from '@/ui/CachedImage';
 import OverlayScrollArea from '@/ui/OverlayScrollArea';
-import { primaryTrackArtistRef } from '@/utils/playback/trackArtistRefs';
+import { primaryTrackArtistRef } from '@/features/playback/utils/playback/trackArtistRefs';
 
 const TOUR_LIMIT = 5;
 const BIO_CLAMP_LINES = 4;

src/features/nowPlaying/components/RadioView.tsx

@@ -2,7 +2,7 @@ import React, { memo } from 'react';
 import { useTranslation } from 'react-i18next';
 import { Cast, Clock, Radio, SkipForward, Users } from 'lucide-react';
 import type { useRadioMetadata } from '@/features/radio';
-import { usePlayerStore } from '@/store/playerStore';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
 import { formatTrackTime } from '@/lib/format/formatDuration';
 
 type NonNullStoreField<K extends keyof ReturnType<typeof usePlayerStore.getState>> =

src/features/nowPlaying/hooks/useNowPlayingPrewarm.test.ts

@@ -5,7 +5,7 @@ import { coverIndexKeyFromRef } from '@/cover/storageKeys';
 import { useNowPlayingPrewarm } from '@/features/nowPlaying/hooks/useNowPlayingPrewarm';
 import { prewarmNowPlayingFetchers } from '@/features/nowPlaying/hooks/useNowPlayingFetchers';
 import { useAuthStore } from '@/store/authStore';
-import { usePlayerStore } from '@/store/playerStore';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
 import { makeTrack } from '@/test/helpers/factories';
 import { resetAllStores } from '@/test/helpers/storeReset';
 import { toQueueItemRefs } from '@/utils/library/queueItemRef';

src/features/nowPlaying/hooks/useNowPlayingPrewarm.ts

@@ -10,9 +10,9 @@ import { coverArtIdFromRadio } from '@/cover/ids';
 import type { CoverArtRef } from '@/cover/types';
 import { prewarmNowPlayingFetchers } from '@/features/nowPlaying/hooks/useNowPlayingFetchers';
 import { useAuthStore } from '@/store/authStore';
-import { usePlayerStore } from '@/store/playerStore';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
 import { usePlaybackServerId } from '@/hooks/usePlaybackServerId';
-import { primaryTrackArtistRef } from '@/utils/playback/trackArtistRefs';
+import { primaryTrackArtistRef } from '@/features/playback/utils/playback/trackArtistRefs';
 
 const NOW_PLAYING_COVER_CSS_PX = 800;
 

src/features/nowPlaying/hooks/useNowPlayingStarLove.ts

@@ -1,7 +1,7 @@
 import { useCallback, useEffect, useState } from 'react';
-import { queueSongStar } from '@/store/pendingStarSync';
+import { queueSongStar } from '@/features/playback/store/pendingStarSync';
 import type { SubsonicSong } from '@/lib/api/subsonicTypes';
-import type { Track } from '@/store/playerStoreTypes';
+import type { Track } from '@/features/playback/store/playerStoreTypes';
 import type { TrackStats } from '@/music-network';
 import { getMusicNetworkRuntime } from '@/music-network';
 

src/features/nowPlaying/pages/NowPlaying.tsx

@@ -8,10 +8,10 @@ import { usePlaybackLibraryNavigate } from '@/hooks/usePlaybackLibraryNavigate';
 import { usePlaybackServerId } from '@/hooks/usePlaybackServerId';
 import { useTranslation } from 'react-i18next';
 import { Music, EyeOff, LayoutGrid, RotateCcw, Eye } from 'lucide-react';
-import { usePlayerStore } from '@/store/playerStore';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
 import { useAuthStore } from '@/store/authStore';
 import { useLyricsStore } from '@/store/lyricsStore';
-import { songToTrack } from '@/utils/playback/songToTrack';
+import { songToTrack } from '@/features/playback/utils/playback/songToTrack';
 import { useRadioMetadata } from '@/features/radio';
 import { useDragDrop } from '@/lib/dnd/DragDropContext';
 import OverlayScrollArea from '@/ui/OverlayScrollArea';
@@ -38,7 +38,7 @@ import DiscographyCard from '@/features/nowPlaying/components/DiscographyCard';
 import { useNowPlayingFetchers } from '@/features/nowPlaying/hooks/useNowPlayingFetchers';
 import { useNowPlayingStarLove } from '@/features/nowPlaying/hooks/useNowPlayingStarLove';
 import { useArtistInfoBatch } from '@/features/artist';
-import { primaryTrackArtistRef, resolveTrackArtistRefs } from '@/utils/playback/trackArtistRefs';
+import { primaryTrackArtistRef, resolveTrackArtistRefs } from '@/features/playback/utils/playback/trackArtistRefs';
 import type { ArtistCardTab } from '@/features/nowPlaying/components/ArtistCard';
 
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