CUB-122: Scaffold Control Center React frontend

frontend/src/pages/SessionsPage.tsx

@@ -0,0 +1,8 @@
+export default function SessionsPage() {
+  return (
+    <div>
+      <h1 className="text-2xl font-bold mb-4">Sessions</h1>
+      <p className="text-on-surface-variant">Active sessions will appear here.</p>
+    </div>
+  )
+}