refactor(api): pull feature-resident subsonic clients into lib/api

Move the 5 subsonic api modules that M3 had co-located into features
(subsonicAlbumInfo/Artists/Playlists/Radio/Statistics) into src/lib/api/, the
feature-free infra layer, and drop their feature-barrel re-exports. Consumers
now import these protocol calls directly from @/lib/api/subsonic*; the feature
barrels export only domain UI/hooks/state.

This is the consistent api placement (plan §10.3, revised: ALL subsonic protocol
clients are feature-free infra, not per-feature) and it kills the documented
api-induced feature<->feature cycles: offline->artist/playlist (getArtist/
getPlaylist*), album->artist (getArtistInfo), deviceSync/nowPlaying/orbit->*.
Remaining artist<->album refs are UI-only (OpenArtistRefInline/coerceOpenArtist
Refs) and offline->playlist is store-level (usePlaylistStore) — both deeper,
tracked for M5, not api placement.

Pure move: import specifiers + vi.mock/spy targets repointed; no behaviour
change. tsc 0, lint 0/0, full suite 319 files / 2353 tests green.

Tooling note: barrel-imported and dynamic-import api symbols were split out of
@/features/* to @/lib/api/* (tsc-driven); 12 vi.mock barrels retargeted to the
deep lib module (mock-collapse sweep), AlbumHeader's UI mock left untouched.

src/features/playlist/utils/playPlaylistById.ts

@@ -1,4 +1,4 @@
-import { getPlaylist } from '@/features/playlist/api/subsonicPlaylists';
+import { getPlaylist } from '@/lib/api/subsonicPlaylists';
 import { songToTrack } from '@/utils/playback/songToTrack';
 import { usePlayerStore } from '@/store/playerStore';
 import { playPlaylistAll } from '@/features/playlist/utils/playlistBulkPlayActions';

src/features/playlist/utils/runPlaylistLoad.ts

@@ -1,5 +1,5 @@
 import type React from 'react';
-import { getPlaylist } from '@/features/playlist/api/subsonicPlaylists';
+import { getPlaylist } from '@/lib/api/subsonicPlaylists';
 import { filterSongsToActiveLibrary } from '@/lib/api/subsonicLibrary';
 import type { SubsonicPlaylist, SubsonicSong } from '@/lib/api/subsonicTypes';
 import { useAuthStore } from '@/store/authStore';

src/features/playlist/utils/runPlaylistSaveMeta.ts

@@ -1,5 +1,5 @@
 import type { TFunction } from 'i18next';
-import { getPlaylist, updatePlaylistMeta, uploadPlaylistCoverArt } from '@/features/playlist/api/subsonicPlaylists';
+import { getPlaylist, updatePlaylistMeta, uploadPlaylistCoverArt } from '@/lib/api/subsonicPlaylists';
 import type { SubsonicPlaylist } from '@/lib/api/subsonicTypes';
 import { showToast } from '@/utils/ui/toast';
 

src/features/playlist/utils/runPlaylistsActions.ts

@@ -1,6 +1,6 @@
 import type React from 'react';
 import type { TFunction } from 'i18next';
-import { deletePlaylist, getPlaylist, updatePlaylist } from '@/features/playlist/api/subsonicPlaylists';
+import { deletePlaylist, getPlaylist, updatePlaylist } from '@/lib/api/subsonicPlaylists';
 import type { SubsonicPlaylist } from '@/lib/api/subsonicTypes';
 import { usePlaylistStore } from '@/features/playlist/store/playlistStore';
 import { showToast } from '@/utils/ui/toast';