Add Spotify lyrics sidecar service and integrate with prefetch

- Add spotify-lyrics-api container to docker-compose
- Update SpotifyLyricsService to use sidecar API
- Prefetch now tries Spotify lyrics first (using track ID), then LRCLib
- Add SPOTIFY_LYRICS_API_URL setting
- Sidecar handles sp_dc cookie authentication automatically

allstarr/Models/Settings/SpotifyApiSettings.cs

@@ -69,4 +69,11 @@ public class SpotifyApiSettings
     /// Used to track cookie age and warn when it's approaching expiration (~1 year).
     /// </summary>
     public string? SessionCookieSetDate { get; set; }
+    
+    /// <summary>
+    /// URL of the Spotify Lyrics API sidecar service.
+    /// Default: http://spotify-lyrics:8080 (docker-compose service name)
+    /// This service wraps Spotify's color-lyrics API for easier access.
+    /// </summary>
+    public string LyricsApiUrl { get; set; } = "http://spotify-lyrics:8080";
 }