refactor(spotify): remove API dependency, use embed scraping only

Spotify client_credentials API access ends 2026-03-06. Remove all
API token/proxy code and the paginated fetch_playlist_with_token
function. Playlist imports now go straight to embed page scraping
(limited to ~50 tracks, no ISRC/album data).

Link resolver for Spotify tracks/albums also switched from API to
embed page scraping via new fetch_embed_metadata function.

Remove Spotify credentials from .env.example since they are no
longer needed.

.env.example

@@ -14,12 +14,6 @@ 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/