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/commands/import_export.rs

@@ -141,3 +141,12 @@ pub async fn restore_db_backup(
         .map_err(|e| format!("Restore failed: {e}"))?
         .map_err(|e: AppError| e.to_string())
 }
+
+/// Rename a database backup file
+#[tauri::command]
+pub fn rename_db_backup(
+    #[allow(non_snake_case)] oldFilename: String,
+    #[allow(non_snake_case)] newName: String,
+) -> Result<String, String> {
+    Database::rename_backup(&oldFilename, &newName).map_err(|e| e.to_string())
+}