Fix null crash on settings page for total_synced field

Backend can return null for total_synced; updated type to reflect this
and added optional chaining to prevent runtime crash.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Sai Sridhar

frontend/lib/types.ts

@@ -145,7 +145,7 @@ export interface GmailStatus {
   connected: boolean;
   email?: string;
   last_sync?: string;
-  total_synced?: number;
+  total_synced?: number | null;
   auth_url?: string;
 }
 

frontend/pages/settings/index.tsx

@@ -668,8 +668,8 @@ function IntegrationsTab({
                   Last synced: {new Date(gmailStatus.last_sync).toLocaleString()}
                 </p>
               )}
-              {gmailStatus.total_synced !== undefined && (
-                <p className="mt-0.5 text-gray-500 dark:text-gray-400">Total emails synced: {gmailStatus.total_synced.toLocaleString()}</p>
+              {gmailStatus.total_synced != null && (
+                <p className="mt-0.5 text-gray-500 dark:text-gray-400">Total emails synced: {gmailStatus.total_synced?.toLocaleString()}</p>
               )}
             </div>
             <button