feat: spotify playlist injection

- Add SpotifyImportSettings configuration model
- Create SpotifyMissingTracksFetcher background service
- Inject virtual Spotify playlists into search results
- Auto-match tracks from external providers
- Update README with feature documentation
- Configure sync window and playlist settings

allstarr/Models/Settings/SpotifyImportSettings.cs

@@ -0,0 +1,69 @@
+namespace allstarr.Models.Settings;
+
+/// <summary>
+/// Configuration for Spotify playlist injection feature.
+/// Requires Jellyfin Spotify Import Plugin: https://github.com/Viperinius/jellyfin-plugin-spotify-import
+/// </summary>
+public class SpotifyImportSettings
+{
+    /// <summary>
+    /// Enable Spotify playlist injection feature
+    /// </summary>
+    public bool Enabled { get; set; }
+    
+    /// <summary>
+    /// Jellyfin server URL (for accessing plugin API)
+    /// </summary>
+    public string JellyfinUrl { get; set; } = string.Empty;
+    
+    /// <summary>
+    /// Jellyfin API key (REQUIRED for accessing missing tracks files)
+    /// Get from Jellyfin Dashboard > API Keys
+    /// </summary>
+    public string ApiKey { get; set; } = string.Empty;
+    
+    /// <summary>
+    /// Hour when Spotify Import plugin runs (24-hour format, 0-23)
+    /// Example: 16 for 4:00 PM
+    /// </summary>
+    public int SyncStartHour { get; set; } = 16;
+    
+    /// <summary>
+    /// Minute when Spotify Import plugin runs (0-59)
+    /// Example: 15 for 4:15 PM
+    /// </summary>
+    public int SyncStartMinute { get; set; } = 15;
+    
+    /// <summary>
+    /// How many hours to search for missing tracks files after sync start time
+    /// Example: 2 means search from 4:00 PM to 6:00 PM
+    /// </summary>
+    public int SyncWindowHours { get; set; } = 2;
+    
+    /// <summary>
+    /// List of playlists to inject
+    /// </summary>
+    public List<SpotifyPlaylistConfig> Playlists { get; set; } = new();
+}
+
+/// <summary>
+/// Configuration for a single Spotify playlist
+/// </summary>
+public class SpotifyPlaylistConfig
+{
+    /// <summary>
+    /// Display name in Jellyfin (e.g., "Release Radar")
+    /// </summary>
+    public string Name { get; set; } = string.Empty;
+    
+    /// <summary>
+    /// Playlist name in Spotify Import plugin missing tracks file
+    /// Must match exactly (e.g., "Release Radar")
+    /// </summary>
+    public string SpotifyName { get; set; } = string.Empty;
+    
+    /// <summary>
+    /// Enable this playlist
+    /// </summary>
+    public bool Enabled { get; set; } = true;
+}