公开页补齐自引用 Canonical 与按类型的结构化数据，图片补上说明文字。

后台设置和内容编辑改成可导航布局；部署用访客 origin 生成 Canonical，避免落到容器地址。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/app/sitemap.ts

@@ -1,22 +1,31 @@
 import type { MetadataRoute } from "next";
+import { connection } from "next/server";
 import {
   fetchPosts,
   fetchAnnouncementsPage,
   fetchPublishedSitePages,
 } from "@/lib/api";
+import { canonicalPath, resolveSiteOrigin } from "@/lib/siteUrl";
 
 export default async function sitemap(): Promise<MetadataRoute.Sitemap> {
-  const baseUrl = "http://localhost:3000";
+  await connection();
+  const origin = resolveSiteOrigin();
+  if (!origin) {
+    console.error("[seo] SITE_URL 缺失或非法，已跳过 sitemap");
+    return [];
+  }
+
+  const url = (pathname: string) => `${origin}${canonicalPath(pathname)}`;
   const entries: MetadataRoute.Sitemap = [
-    { url: `${baseUrl}/`, lastModified: new Date(), changeFrequency: "daily", priority: 1 },
+    { url: url("/"), lastModified: new Date(), changeFrequency: "daily", priority: 1 },
     {
-      url: `${baseUrl}/announcements`,
+      url: url("/announcements"),
       lastModified: new Date(),
       changeFrequency: "daily",
       priority: 0.7,
     },
     {
-      url: `${baseUrl}/about`,
+      url: url("/about"),
       lastModified: new Date(),
       changeFrequency: "monthly",
       priority: 0.6,
@@ -27,7 +36,7 @@ export default async function sitemap(): Promise<MetadataRoute.Sitemap> {
     const { posts } = await fetchPosts(1, 100);
     for (const post of posts) {
       entries.push({
-        url: `${baseUrl}/post/${post.id}`,
+        url: url(`/post/${post.id}`),
         lastModified: new Date(post.created_at),
         changeFrequency: "weekly",
         priority: 0.6,
@@ -41,7 +50,7 @@ export default async function sitemap(): Promise<MetadataRoute.Sitemap> {
     const { announcements } = await fetchAnnouncementsPage(1, 100);
     for (const a of announcements) {
       entries.push({
-        url: `${baseUrl}/announcement/${a.id}`,
+        url: url(`/announcement/${a.id}`),
         lastModified: new Date(a.updated_at || a.created_at),
         changeFrequency: "weekly",
         priority: 0.5,
@@ -55,7 +64,7 @@ export default async function sitemap(): Promise<MetadataRoute.Sitemap> {
     const { pages } = await fetchPublishedSitePages();
     for (const p of pages) {
       entries.push({
-        url: `${baseUrl}/p/${p.slug}`,
+        url: url(`/p/${p.slug}`),
         lastModified: new Date(p.updated_at || p.created_at),
         changeFrequency: "monthly",
         priority: 0.4,