List the action's rejected fields above the register form

web/frontend/app/features/auth/components/AuthErrorAlert.tsx

@@ -1,10 +1,20 @@
 interface AuthErrorAlertProps {
     message: string;
+    /** Per-field messages to list beneath the summary. */
+    details?: readonly string[];
 }
 
-const AuthErrorAlert = ({ message }: AuthErrorAlertProps) => (
-    <div role="alert" className="alert alert-error alert-soft">
+const AuthErrorAlert = ({ message, details }: AuthErrorAlertProps) => (
+    <div role="alert" className="alert alert-error alert-soft flex-col items-start">
         <span>{message}</span>
+
+        {details?.length ? (
+            <ul className="list-inside list-disc text-sm">
+                {details.map((detail) => (
+                    <li key={detail}>{detail}</li>
+                ))}
+            </ul>
+        ) : null}
     </div>
 );