src: first layout, many dependencies

- setup query templates and potential auth flow/state
- basic server & channel lists
- guessed types for db and apis
- user panel / settings templates
- many steps left

concord-client/src/pages/NotFoundPage.tsx

@@ -0,0 +1,12 @@
+const NotFoundPage: React.FC = () => {
+  return (
+    <div className="min-h-screen bg-gray-900 flex items-center justify-center">
+      <div className="text-center text-gray-400">
+        <h1 className="text-4xl font-bold mb-4">404</h1>
+        <p className="text-xl">Page not found</p>
+      </div>
+    </div>
+  );
+};
+
+export default NotFoundPage;