feat(web): add error boundaries to uncovered route groups

Root, auth, invite, and setup routes now have error.tsx files,
ensuring every Next.js page route has error boundary coverage.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/src/app/invite/error.tsx

@@ -0,0 +1,14 @@
+"use client";
+export default function InviteError({ error, reset }: { error: Error; reset: () => void }) {
+  return (
+    <div className="flex min-h-screen items-center justify-center p-6">
+      <div className="text-center">
+        <h2 className="text-lg font-semibold">Something went wrong</h2>
+        <p className="mt-1 text-sm text-gray-500">{error.message}</p>
+        <button onClick={reset} className="mt-4 rounded bg-blue-600 px-4 py-2 text-white">
+          Try again
+        </button>
+      </div>
+    </div>
+  );
+}