feat(01-02): build agent portal layout, dashboard stub, and logout mechanism

- LogoutButton: client component with server action calling signOut to ?signed_out=1
- AgentLayout: defense-in-depth auth() check, header with email and sign-out button
- DashboardPage: belt-and-suspenders auth() check, welcome message with agent email
- HomePage: updated to Teressa Copeland Homes placeholder (Phase 2 marketing site)
- npm run build and npx tsc --noEmit both pass with zero errors

teressa-copeland-homes/src/components/ui/LogoutButton.tsx

@@ -0,0 +1,19 @@
+import { signOut } from "@/lib/auth";
+
+async function logoutAction() {
+  "use server";
+  await signOut({ redirectTo: "/agent/login?signed_out=1" });
+}
+
+export function LogoutButton() {
+  return (
+    <form action={logoutAction}>
+      <button
+        type="submit"
+        className="text-sm text-gray-600 hover:text-gray-900 underline"
+      >
+        Sign out
+      </button>
+    </form>
+  );
+}