feat(backup): add independent backup panel, configurable policy, and rename support

Extract backup & restore into a standalone AccordionItem in Advanced settings.
Add configurable auto-backup interval (disabled/6h/12h/24h/48h/7d) and retention
count (3-50) via settings. Add per-backup rename with inline editing UI.

src-tauri/src/lib.rs

@@ -903,6 +903,7 @@ pub fn run() {
             commands::open_zip_file_dialog,
             commands::list_db_backups,
             commands::restore_db_backup,
+            commands::rename_db_backup,
             commands::sync_current_providers_live,
             // Deep link import
             commands::parse_deeplink,