docs: update README — importer sources, metadata editor, file conventions, project structure

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -22,6 +22,7 @@ Built with Vite + vanilla ES modules, served via nginx in Docker.
 
 ### Playback
 - Queue management with shuffle, repeat (all / once), and radio mode (endless random)
+- Spotify-style shuffle — pre-shuffles the full queue so every song plays exactly once
 - Now Playing overlay with swipe-to-dismiss; queue tab stays active when selecting a song from the queue
 - Lock screen media controls (Android / iOS via Media Session API)
 - Gapless-style queue with prev/next, skip forward/back
@@ -29,13 +30,24 @@ Built with Vite + vanilla ES modules, served via nginx in Docker.
 
 ### Discovery
 - iTunes / Last.fm integration — charts, global search, 30-second previews, similar artists, recommendations
-- Spotify playlist importer — paste a Spotify playlist URL to preview and download all tracks, enriched with iTunes metadata and cover art
+- Song Importer — paste a link from Spotify, YouTube, YouTube Music, or SoundCloud to preview and download tracks, enriched with iTunes metadata and cover art
 
 ### Downloads (yt-dlp backend)
-- Download individual tracks, full albums, or entire artists from YouTube / SoundCloud
-- Spotify playlist importer downloads with iTunes-enriched metadata (album, year, track number, genre, cover art)
+- Download individual tracks, full albums, or entire artists
+- Sources: YouTube Music (primary), YouTube, SoundCloud, Spotify (via playlist importer)
+- iTunes enrichment — album, year, track number, genre, 1000×1000 cover art
 - Duplicate detection — skips tracks already present on the server
-- Lyrics embedded into downloaded files (LRCLIB)
+- Standard filename convention: `{01 - }Artist1, Artist2 - Title.ext`
+- Files organised into `MusicRoot/AlbumArtist/Album/` folders automatically
+
+### Metadata Editor
+- Edit title, artist, album artist, album, genre, year, track number, disc number from within the app
+- Update embedded cover art via URL or file upload
+- Artist separator normalization — accepts `•`, `;`, `,` as input; stores as `;` (Navidrome/MusicBrainz style)
+- File renamed automatically on save to match the standard naming convention
+- File moved to the correct `AlbumArtist/Album/` folder when those fields change
+- Empty folders cleaned up after a move
+- Navidrome rescan triggered automatically after every save
 
 ### Playlists
 - Create, edit, and delete playlists
@@ -67,18 +79,27 @@ Music_App/
 │   ├── api.js                 # Subsonic API, Navidrome REST, iTunes API
 │   ├── player.js              # Playback, transport, queue, media session, preview
 │   ├── views.js               # Navigation, page loaders, card makers, search
-│   ├── ui.js                  # Modals, overlays, sidebar, settings, context menu
+│   ├── ui.js                  # Modals, overlays, sidebar, settings, context menu, metadata editor
 │   ├── nowplaying.js          # Now Playing overlay
 │   ├── abs.js                 # Audiobookshelf integration
-│   ├── spotify.js             # Spotify playlist importer
-│   ├── components.js          # Shared UI components
+│   ├── spotify.js             # Spotify importer (resolve + download)
+│   ├── youtube.js             # YouTube / YouTube Music importer
+│   ├── soundcloud.js          # SoundCloud importer
+│   ├── components.js          # Shared UI components (song rows, cards)
 │   ├── themes.js              # Theme switching
 │   ├── pwa.js                 # Service worker registration + update banner
 │   └── main.js                # App init, audio wiring, window globals
 ├── backend/
-│   ├── novasonic-server.js    # Node.js download backend (yt-dlp + ffmpeg)
+│   ├── novasonic-server.js    # Express API: download jobs, metadata edit, resolvers
+│   ├── spotify_resolve.py     # Spotify page scraper (track/album/playlist metadata)
 │   └── lib/
-│       └── metadata.js        # iTunes lookup, lyrics fetch, artwork download
+│       ├── config.js          # Backend config (env vars, paths, format)
+│       ├── jobs.js            # In-memory job store + log helper
+│       ├── metadata.js        # iTunes lookup, artwork download, lyrics fetch, filename helpers
+│       ├── ytdlp.js           # yt-dlp download cascade + ffmpeg metadata embedding
+│       ├── squid.js           # Squid/Qobuz download backend
+│       ├── downloader.js      # Unified downloadTrack / downloadAlbumTracks entry point
+│       └── romaji.js          # Japanese → romaji index for search
 ├── public/                    # Static assets (copied as-is to dist/)
 │   ├── sw.js                  # Service worker
 │   ├── manifest.json          # PWA manifest