docs: update README and add AUR automation

- Add installation instructions (AUR, Flatpak, AppImage)
- Document all API keys (Last.fm, Discogs, Spotify, Tidal)
- Add playlist import feature documentation
- Update project structure
- Add PKGBUILD for qbz-bin AUR package
- Add workflow to auto-update AUR on release
- Update .env.example with Spotify/Tidal variables

.env.example

@@ -13,3 +13,17 @@ LAST_FM_APP_REGISTER=your_lastfm_username
 
 DISCOGS_API_CLIENT_KEY=your_consumer_key_here
 DISCOGS_API_CLIENT_SECRET=your_consumer_secret_here
+
+# Spotify API Configuration (for playlist import)
+# Create your own Spotify application at: https://developer.spotify.com/dashboard
+# These credentials are used for importing playlists from Spotify
+
+SPOTIFY_API_CLIENT_ID=your_client_id_here
+SPOTIFY_API_CLIENT_SECRET=your_client_secret_here
+
+# Tidal API Configuration (for playlist import)
+# Create your own Tidal application at: https://developer.tidal.com/
+# These credentials are used for importing playlists from Tidal
+
+TIDAL_API_CLIENT_ID=your_client_id_here
+TIDAL_API_CLIENT_SECRET=your_client_secret_here