SEO 全链路：OG/Twitter 标签 + robots.txt + sitemap.xml + JSON-LD 结构化数据

- layout metadata: Open Graph + Twitter Card + canonical + robots 指令
- app/robots.ts: 允许首页/auth，禁止 /terminal/account/ops/api
- app/sitemap.ts: 首页 1.0 + /auth/login 0.6
- 首页 JSON-LD: WebApplication schema，含 $10/mo 定价

frontend/app/robots.ts

@@ -0,0 +1,14 @@
+import type { MetadataRoute } from "next";
+
+export default function robots(): MetadataRoute.Robots {
+  return {
+    rules: [
+      {
+        userAgent: "*",
+        allow: "/",
+        disallow: ["/terminal/", "/account/", "/ops/", "/api/"],
+      },
+    ],
+    sitemap: "https://polyweather.top/sitemap.xml",
+  };
+}