feat: notification batching, per-folder mute, and global pause

Debounce embedding/tagging completion notifications per folder (6s window)
so rapid file additions from downloaders fire one notification instead of
one per file. Add per-folder mute via the sidebar context menu and a global
pause toggle in Settings > General, both persisted across restarts.

src-tauri/src/lib.rs

@@ -148,6 +148,10 @@ pub fn run() {
             commands::vacuum_database,
             commands::get_orphaned_thumbnails_info,
             commands::cleanup_orphaned_thumbnails,
+            commands::get_muted_folder_ids,
+            commands::set_muted_folder_ids,
+            commands::get_notifications_paused,
+            commands::set_notifications_paused,
         ])
         .run(tauri::generate_context!())
         .expect("error while running tauri application");