refactor: reuse Jellyfin settings for Spotify feature

- Remove duplicate JellyfinUrl and ApiKey from SpotifyImportSettings
- Use existing JELLYFIN_URL and JELLYFIN_API_KEY settings
- Simplify configuration - no duplicate settings needed
- Update documentation and .env.example

allstarr/Models/Settings/SpotifyImportSettings.cs

@@ -3,6 +3,7 @@ namespace allstarr.Models.Settings;
 /// <summary>
 /// Configuration for Spotify playlist injection feature.
 /// Requires Jellyfin Spotify Import Plugin: https://github.com/Viperinius/jellyfin-plugin-spotify-import
+/// Uses JellyfinSettings.Url and JellyfinSettings.ApiKey for API access.
 /// </summary>
 public class SpotifyImportSettings
 {
@@ -11,17 +12,6 @@ public class SpotifyImportSettings
     /// </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