UNAUTHORIZED gmail error (#12262)

# Gmail OAuth authentication flow issues

### TLDR
This error is not an error and therefore should be treated as a simple
redirect with a snackbar.

### More details
Fixing incomplete OAuth token exchange processes and improving error
handling for empty Gmail inboxes.
The changes include modifications to OAuth guards, to ensure that if a
user clicks "cancel" instead of completing the authentication workflow
if fails

## Before:
Redirection from `/settings/accounts` to `app.twenty.com` with an
`UNAUTHORIZED` error

## After :
<img width="948" alt="Screenshot 2025-05-26 at 18 04 37"
src="https://github.com/user-attachments/assets/62c8721e-c2b3-4e3d-ad0b-e4059dfb7a98"
/>


Fixes https://github.com/twentyhq/twenty/issues/11895

---------

Co-authored-by: Charles Bochet <charles@twenty.com>

packages/twenty-front/src/modules/error-handler/components/ErrorMessageEffect.tsx

@@ -0,0 +1,26 @@
+import { useEffect } from 'react';
+
+import { SnackBarVariant } from '@/ui/feedback/snack-bar-manager/components/SnackBar';
+import { useSnackBar } from '@/ui/feedback/snack-bar-manager/hooks/useSnackBar';
+import { useSearchParams } from 'react-router-dom';
+import { isDefined } from 'twenty-shared/utils';
+
+export const ErrorMessageEffect = () => {
+  const { enqueueSnackBar } = useSnackBar();
+  const [searchParams, setSearchParams] = useSearchParams();
+  const errorMessage = searchParams.get('errorMessage');
+
+  useEffect(() => {
+    if (isDefined(errorMessage)) {
+      enqueueSnackBar(errorMessage, {
+        dedupeKey: 'error-message-dedupe-key',
+        variant: SnackBarVariant.Error,
+      });
+      const newSearchParams = new URLSearchParams(searchParams);
+      newSearchParams.delete('errorMessage');
+      setSearchParams(newSearchParams);
+    }
+  }, [enqueueSnackBar, errorMessage, searchParams, setSearchParams]);
+
+  return <></>;
+};