Fix seasonal playlists not appearing when Deezer is active source

_get_source() hardcoded 'itunes' as fallback, so seasonal content was
stored with source='itunes' but API endpoints queried source='deezer' —
resulting in empty discover page seasons. Now reads the configured
fallback source from metadata_service.

core/seasonal_discovery.py

@@ -99,7 +99,11 @@ class SeasonalDiscoveryService:
         """Determine active music source (matches _get_active_discovery_source in web_server)"""
         if self.spotify_client and self.spotify_client.is_spotify_authenticated():
             return 'spotify'
-        return 'itunes'
+        try:
+            from core.metadata_service import _get_configured_fallback_source
+            return _get_configured_fallback_source()
+        except Exception:
+            return 'itunes'
 
     def _ensure_database_schema(self):
         """Create seasonal content tables if they don't exist"""