Please address the comments from this code review:
## Overall Comments
- There are unresolved Git conflict markers in AuthSignInBox.tsx (<<<<<<< HEAD / >>>>>>>); please remove them and finalize the intended callbackUrl logic.
- Enhance the fetcher in LobeNextAuthDbAdapter to check response.ok and throw or handle HTTP errors before parsing JSON to avoid unexpected failures.
- Add request validation (e.g. with Zod) in the /api/auth/adapter route to enforce correct action names and payload shapes and prevent malformed requests.

## Individual Comments

### Comment 1
<location> `src/libs/next-auth/adapter/index.ts:42` </location>
<code_context>
+    throw new Error('LobeNextAuthDbAdapter: KEY_VAULTS_SECRET is not set in environment variables');
+  }
+
+  const fetcher = (action: string, data: any) => fetch(interactionUrl, {
+    method: 'POST',
+    headers: {
</code_context>

<issue_to_address>
No retry or error handling for network failures in fetcher.

Add try/catch and handle network errors, timeouts, and non-JSON responses to prevent unhandled promise rejections and improve error clarity.
</issue_to_address>

### Comment 2
<location> `src/libs/next-auth/adapter/index.ts:79` </location>
<code_context>
-        .delete(nextauthSessions)
-        .where(eq(nextauthSessions.sessionToken, sessionToken));
+      const result = await fetcher('deleteSession', sessionToken);
+      await postProcessor(result);
       return;
     },
</code_context>

<issue_to_address>
deleteSession and deleteUser do not return deleted objects as per Adapter contract.

The current implementation always returns undefined, which may break consumers relying on the deleted object. Please return the deleted object or null if not found, as required by the Adapter contract.
</issue_to_address>

### Comment 3
<location> `src/libs/next-auth/adapter/index.ts:145` </location>
<code_context>
-            eq(nextauthAccounts.providerAccountId, account.providerAccountId),
-          ),
-        );
+      const result = await fetcher('unlinkAccount', account);
+      await postProcessor(result);
+      return
</code_context>

<issue_to_address>
unlinkAccount does not return AdapterAccount as per Adapter contract.

Currently, unlinkAccount always returns undefined. To align with the Adapter contract and avoid issues for consumers expecting the deleted AdapterAccount, return the deleted account when available.
</issue_to_address>

### Comment 4
<location> `src/app/(backend)/api/auth/adapter/route.ts:93` </location>
<code_context>
+        }
+        return NextResponse.json({ success: true, data: result });
+    } catch (error) {
+        return NextResponse.json({ success: false, error }, { status: 400 });
+    }
+}
</code_context>

<issue_to_address>
Error responses may leak internal error objects.

Avoid returning raw error objects; instead, return sanitized error messages to prevent exposing sensitive information.
</issue_to_address>

### Comment 5
<location> `src/app/[variants]/(auth)/next-auth/signin/AuthSignInBox.tsx:78` </location>
<code_context>

   const searchParams = useSearchParams();

+<<<<<<< HEAD
   // Redirect back to the page url, fallback to '/' if failed
+=======
+  // Redirect back to the page url
+>>>>>>> ecf695d9b (:bug: fix: default callbackUrl)
   const callbackUrl = searchParams.get('callbackUrl') ?? '/';

</code_context>

<issue_to_address>
Unresolved merge conflict markers present in code.

Please resolve the merge conflict markers (<<<<<<<, =======, >>>>>>>) to prevent syntax errors before merging.
</issue_to_address>