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/sitemap.ts

@@ -0,0 +1,20 @@
+import type { MetadataRoute } from "next";
+
+export default function sitemap(): MetadataRoute.Sitemap {
+  const baseUrl = "https://polyweather.top";
+
+  return [
+    {
+      url: baseUrl,
+      lastModified: new Date(),
+      changeFrequency: "weekly",
+      priority: 1.0,
+    },
+    {
+      url: `${baseUrl}/auth/login`,
+      lastModified: new Date(),
+      changeFrequency: "monthly",
+      priority: 0.6,
+    },
+  ];
+}