Show update UI on backup version mismatch

ts/services/backups/errors.ts

@@ -0,0 +1,10 @@
+// Copyright 2024 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import type Long from 'long';
+
+export class UnsupportedBackupVersion extends Error {
+  constructor(version: Long) {
+    super(`Unsupported backup version: ${version}`);
+  }
+}