refactor: migrate from pnpm workspaces to single-package structure with shared types

client/app/page.tsx

@@ -0,0 +1,18 @@
+import Link from 'next/link';
+
+export default function HomePage() {
+  return (
+    <main className="landing">
+      <section className="panel">
+        <h1>YouTube Chat Client</h1>
+        <p>
+          Launch the dashboard to monitor live chat and control the overlay that feeds OBS.
+        </p>
+        <Link className="primary" href="/dashboard">
+          Open Dashboard
+        </Link>
+        <p className="muted">Overlay preview lives at /overlay for the OBS browser source.</p>
+      </section>
+    </main>
+  );
+}