fix: add type guard for detail property in error data

- Check for 'detail' property before accessing it
- Maintain all error handling functionality
- Ensure TypeScript type safety

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

web/src/pages/SettingsPage.tsx

@@ -230,7 +230,7 @@ function SettingsForm({ me, onBack }: { me: MemberRead; onBack: () => void }) {
                   } else if (typeof err === 'object' && err !== null && 'status' in err && 'data' in err) {
                     // Try to extract more details from the error object
                     console.error("Error details:", JSON.stringify(err));
-                    if (err.status === 422 && err.data && err.data.detail) {
+                    if (err.status === 422 && err.data && 'detail' in err.data) {
                       errorMessage = err.data.detail;
                     }
                   }