feat(settings): add orphaned thumbnail cleanup to General section

Scans the thumbnails directory and cross-references against thumbnail_path
values in the images table, deleting any files not linked to an indexed image.
Surfaces count and reclaimable MB in the General section alongside the
existing Compact database card.

src-tauri/src/lib.rs

@@ -146,6 +146,8 @@ pub fn run() {
             commands::open_app_data_folder,
             commands::get_database_info,
             commands::vacuum_database,
+            commands::get_orphaned_thumbnails_info,
+            commands::cleanup_orphaned_thumbnails,
         ])
         .run(tauri::generate_context!())
         .expect("error while running tauri application");