feat: move the whole metadata/search stack from iTunes to Deezer (1.3)

Apple's iTunes /search returns 403 from server/datacenter IPs, which had broken global
search, charts, album/artist/single downloads and the metadata-editor autofill in
production. Everything now sources metadata from Deezer (free, no key, more requests,
returns explicit versions + real artist images + durations). Web + Android share one
source, so an artist resolves to one consistent name everywhere. Deezer results are
mapped to the legacy "ItunesItem" shape, so the UI + download flow are unchanged.

Backend:
- New backend/lib/deezer.js: lookupTrackMeta, fetchAlbumTracks, searchAlbumTracks,
  fetchArtistAlbums (+ pure pickTrackMatch/mapAlbumTrack for tests).
- metadata.js drops the iTunes lookups; novasonic-server download paths (track, album,
  artist, playlist enrich, spotify artwork) + autofill now use Deezer.
- Artist download uses Deezer discography (real albums only), not the iTunes album search.
- Editor autofill endpoint /api/itunes/lookup -> /api/meta/lookup; removed the dead
  iTunes /search proxy and the Apple charts RSS proxy.
- backend/test/deezer.test.js: unit tests for numbering, mixed-artist album-artist
  stability, explicit flags, the Japanese-title match guard (npm test; RUN_LIVE=1 for live).

Web:
- api.js search/lookups already on Deezer; charts now use Deezer /chart. Artist cards
  show the real Deezer photo. Visible "iTunes"/"Apple Music" labels -> "Deezer"
  (search badge, charts badge, preview bar, editor button, artist heading). SW ns-v51.

Android:
- New DeezerModels.kt with Dz* models + mappers to ItunesItem/ItunesRssEntry.
- ItunesClient is Deezer-backed (search = tracks+albums+artists in parallel; album/artist
  lookups; /chart charts), same method signatures. Visible strings -> Deezer.

Docs: README, CLAUDE.md and CHANGELOG (1.3) updated; Platform Parity Matrix reflects the
shared Deezer source + Android non-local artist page.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -10,9 +10,9 @@ Built with Vite + vanilla ES modules (web) and Jetpack Compose + Media3/ExoPlaye
 - **Library** — Stream from Navidrome / Subsonic; browse artists, albums, playlists, genres, starred, and random; search; star + context menu on every row.
 - **Playback** — Queue with shuffle, repeat, and radio mode (endless similar songs); gapless-style preload; lock-screen / notification controls; Navidrome scrobbling.
 - **Lyrics** — Synced and plain lyrics via lrclib.net, auto-fetched and cached per session.
-- **Artist pages** — Hero card, Last.fm bio / similar / top songs, Ticketmaster events, and iTunes cross-reference showing owned vs. missing tracks.
+- **Artist pages** — Hero card, Last.fm bio / similar / top songs, Ticketmaster events, and a Deezer cross-reference showing owned vs. missing tracks.
 - **Playlists** — Create, rename, delete, add/remove tracks, and upload a cover (Web + Android).
-- **Importer & downloads** — Paste a Spotify / YouTube / YouTube Music / SoundCloud link to download via yt-dlp, with iTunes metadata enrichment and duplicate detection.
+- **Importer & downloads** — Paste a Spotify / YouTube / YouTube Music / SoundCloud link to download via yt-dlp, with Deezer metadata enrichment and duplicate detection.
 - **Metadata editor** (web) — Edit tags + cover art; files are renamed/moved and Navidrome is rescanned on save.
 - **Offline** (Android) — Download albums, playlists, or single songs to private storage; an Offline tab to play and manage them (works without a server connection); downloaded tracks play from disk on every screen.
 - **Audiobookshelf** — Browse and stream audiobooks with chapter navigation, speed control, sleep timer, and progress sync.
@@ -51,20 +51,21 @@ NovaSonic/
 │   │   └── settings.js        # Settings page
 │   ├── state.js               # Shared mutable state (S object)
 │   ├── utils.js               # Helpers (md5, esc, formatDur, toast)
-│   ├── api.js                 # Subsonic API, iTunes API, cover art
+│   ├── api.js                 # Subsonic API, Deezer API, cover art
 │   └── main.js                # App init, audio wiring, window globals
 ├── backend/
 │   ├── novasonic-server.js    # Express API: downloads, metadata, events proxy, ABS proxy
 │   └── lib/
 │       ├── config.js          # Env var → config object
 │       ├── jobs.js            # In-memory download job store
-│       ├── metadata.js        # iTunes lookup, artwork, filename helpers
+│       ├── deezer.js          # Deezer metadata: track/album/artist lookups
+│       ├── metadata.js        # Artwork, filename helpers, duplicate detection
 │       ├── ytdlp.js           # yt-dlp download + ffmpeg metadata embedding
 │       ├── downloader.js      # Unified downloadTrack / downloadAlbumTracks
 │       └── romaji.js          # Japanese → romaji search index
 ├── android/                   # Native Android app (Jetpack Compose + Media3)
 │   └── app/src/main/kotlin/com/novasonic/app/
-│       ├── api/               # SubsonicClient, AbsClient, LrcLibClient, ItunesClient
+│       ├── api/               # SubsonicClient, AbsClient, LrcLibClient, ItunesClient (Deezer-backed)
 │       ├── data/              # PrefsStore (DataStore), MusicRepository, StarState
 │       ├── offline/           # Room DB, DAO, OfflineRepository, DownloadWorker (offline downloads)
 │       ├── player/            # PlayerController, MusicService (Media3)