feat: add ads/sponsor/captcha modules and polish home & chat UI

frontend/app/ads/buy/page.tsx

@@ -0,0 +1,15 @@
+import type { Metadata } from "next";
+import AdsBuyClient from "./AdsBuyClient";
+import { requestCanonical } from "@/lib/canonicalMeta";
+
+export async function generateMetadata(): Promise<Metadata> {
+  return {
+    title: "自助购买广告位",
+    description: "在首页侧栏投放图片或文字推广，支持游客申购。",
+    ...(await requestCanonical("/ads/buy")),
+  };
+}
+
+export default function AdsBuyPage() {
+  return <AdsBuyClient />;
+}