fix(analyze): restore connectivity_provider import for drain()

Removed in f6ee837 thinking it was unused, but drain() still
reads connectivityProvider.future to gate replay attempts.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

flutter_client/lib/cache/mutation_queue.dart

@@ -38,6 +38,7 @@ import '../playlists/playlists_provider.dart' show playlistsApiProvider;
 import '../quarantine/quarantine_provider.dart' show quarantineApiProvider;
 import '../requests/requests_provider.dart' show requestsApiProvider;
 import 'audio_cache_manager.dart' show appDbProvider;
+import 'connectivity_provider.dart';
 import 'db.dart';
 
 /// Stable kind constants. Each controller emits one of these via