fix(storage): allow staging local config when S3 is unreachable

When switching storage drivers in admin settings, save now validates
connectivity against the selected target backend instead of retesting
the still-active driver. The active driver remains unchanged until
migration completes, so unreachable MinIO no longer blocks saving local
storage settings.

frontend/app/(main)/admin/files/components/storage-config-tab.tsx

@@ -149,13 +149,8 @@ export function StorageConfigTab() {
 
   const saveMutation = useMutation({
     mutationFn: async (value: StorageConfig) => {
-      const activeDriver = query.data?.config.driver || value.driver
-      const valueToSave = {
-        ...value,
-        driver: activeDriver,
-      }
       await services.adminSystemConfig.updateSystemConfig(storageConfigKey, {
-        value: JSON.stringify(valueToSave),
+        value: JSON.stringify(value),
       })
     },
     onSuccess: () => {