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/favorites/components/FavoriteSongRow.tsx

@@ -9,7 +9,7 @@ import i18n from '@/lib/i18n';
 import { formatTrackTime } from '@/lib/format/formatDuration';
 import StarRating from '@/components/StarRating';
 import { OpenArtistRefInline } from '@/features/artist';
-import { resolveTrackArtistRefs } from '@/utils/playback/trackArtistRefs';
+import { resolveTrackArtistRefs } from '@/features/playback/utils/playback/trackArtistRefs';
 
 export interface FavoriteSongRowCallbacks {
   activate: (song: SubsonicSong, index: number, e: React.MouseEvent) => void;

src/features/favorites/components/FavoritesSongsSectionHeader.tsx

@@ -2,9 +2,9 @@ import React, { useMemo, useRef } from 'react';
 import { useTranslation } from 'react-i18next';
 import { ListPlus, Play, SlidersHorizontal, X } from 'lucide-react';
 import type { SubsonicSong } from '@/lib/api/subsonicTypes';
-import { usePlayerStore } from '@/store/playerStore';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
 import { useSelectionStore } from '@/store/selectionStore';
-import { songToTrack } from '@/utils/playback/songToTrack';
+import { songToTrack } from '@/features/playback/utils/playback/songToTrack';
 import { AddToPlaylistSubmenu } from '@/components/ContextMenu';
 import GenreFilterBar from '@/components/GenreFilterBar';
 

src/features/favorites/components/FavoritesSongsTracklist.tsx

@@ -6,13 +6,13 @@ import { useTranslation } from 'react-i18next';
 import { useNavigate } from 'react-router-dom';
 import type { ColDef } from '@/utils/useTracklistColumns';
 import type { SubsonicSong } from '@/lib/api/subsonicTypes';
-import { usePlayerStore } from '@/store/playerStore';
-import { previewInputFromSong, usePreviewStore } from '@/store/previewStore';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
+import { previewInputFromSong, usePreviewStore } from '@/features/playback/store/previewStore';
 import { useSelectionStore } from '@/store/selectionStore';
 import { useThemeStore } from '@/store/themeStore';
 import { useDragDrop } from '@/lib/dnd/DragDropContext';
 import { useOrbitSongRowBehavior } from '@/features/orbit';
-import { songToTrack } from '@/utils/playback/songToTrack';
+import { songToTrack } from '@/features/playback/utils/playback/songToTrack';
 import { appendServerQuery } from '@/utils/navigation/detailServerScope';
 import { APP_MAIN_SCROLL_VIEWPORT_ID } from '@/constants/appScroll';
 import { useElementClientHeightById } from '@/lib/hooks/useResizeClientHeight';

src/features/favorites/hooks/useFavoritesData.ts

@@ -5,7 +5,7 @@ import type {
   InternetRadioStation, SubsonicAlbum, SubsonicArtist, SubsonicSong,
 } from '@/lib/api/subsonicTypes';
 import { useAuthStore } from '@/store/authStore';
-import { usePlayerStore } from '@/store/playerStore';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
 import type { TopFavoriteArtist } from '@/features/favorites/components/TopFavoriteArtists';
 import { useConnectionStatus } from '@/hooks/useConnectionStatus';
 import { isActiveServerReachable } from '@/utils/network/activeServerReachability';

src/features/favorites/hooks/useFavoritesSongFiltering.tsx

@@ -1,7 +1,7 @@
 import React, { useMemo } from 'react';
 import { ArrowDown, ArrowUp } from 'lucide-react';
 import type { SubsonicSong } from '@/lib/api/subsonicTypes';
-import { usePlayerStore } from '@/store/playerStore';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
 
 const CURRENT_YEAR = new Date().getFullYear();
 const MIN_YEAR = 1950;

src/features/favorites/pages/Favorites.tsx

@@ -1,4 +1,4 @@
-import { queueSongStar, queueSongRating } from '@/store/pendingStarSync';
+import { queueSongStar, queueSongRating } from '@/features/playback/store/pendingStarSync';
 import React, { useEffect, useMemo, useState } from 'react';
 import { useTracklistColumns, type ColDef } from '@/utils/useTracklistColumns';
 import { TopFavoriteArtistsRow } from '@/features/favorites/components/TopFavoriteArtists';
@@ -11,7 +11,7 @@ import { useFavoritesSelection } from '@/features/favorites/hooks/useFavoritesSe
 import { useBulkPlPickerOutsideClick } from '@/hooks/useBulkPlPickerOutsideClick';
 import { AlbumRow } from '@/features/album';
 import { ArtistRow } from '@/features/artist';
-import { usePlayerStore } from '@/store/playerStore';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
 import { useTranslation } from 'react-i18next';
 import { useSelectionStore } from '@/store/selectionStore';
 import FavoritesOfflineHeader from '@/features/favorites/components/FavoritesOfflineHeader';