Add the split-screen auth shell and its card components

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

@@ -0,0 +1,18 @@
+import { Link } from 'react-router';
+
+interface AuthSwitchPromptProps {
+    lead: string;
+    to: string;
+    label: string;
+}
+
+const AuthSwitchPrompt = ({ lead, to, label }: AuthSwitchPromptProps) => (
+    <p className="text-center text-[0.9375rem] text-[var(--color-muted)]">
+        {lead}{' '}
+        <Link to={to} className="font-semibold text-secondary hover:text-primary">
+            {label}
+        </Link>
+    </p>
+);
+
+export default AuthSwitchPrompt;