feat: 站点单页、时间线导入与行级 BBCode 短代码

首页右栏接入单页入口与公告置顶/全部页；Markdown 编辑器支持可视化时间线与 Git 导入；隐藏块改为 [hide]/[timeline] 命名闭合，并修复单页/公告 GORM 更新只改 updated_at 的问题。

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

frontend/app/sitemap.ts

@@ -1,10 +1,16 @@
 import type { MetadataRoute } from "next";
-import { fetchPosts } from "@/lib/api";
+import { fetchPosts, fetchAnnouncementsPage, fetchOverview } from "@/lib/api";
 
 export default async function sitemap(): Promise<MetadataRoute.Sitemap> {
   const baseUrl = "http://localhost:3000";
   const entries: MetadataRoute.Sitemap = [
     { url: `${baseUrl}/`, lastModified: new Date(), changeFrequency: "daily", priority: 1 },
+    {
+      url: `${baseUrl}/announcements`,
+      lastModified: new Date(),
+      changeFrequency: "daily",
+      priority: 0.7,
+    },
   ];
 
   try {
@@ -21,5 +27,34 @@ export default async function sitemap(): Promise<MetadataRoute.Sitemap> {
     /* 忽略 API 错误 */
   }
 
+  try {
+    const { announcements } = await fetchAnnouncementsPage(1, 100);
+    for (const a of announcements) {
+      entries.push({
+        url: `${baseUrl}/announcement/${a.id}`,
+        lastModified: new Date(a.updated_at || a.created_at),
+        changeFrequency: "weekly",
+        priority: 0.5,
+      });
+    }
+  } catch {
+    /* 忽略 */
+  }
+
+  // 公开单页列表 API 尚未提供：用 overview 侧栏页近似收录已发布且展示中的页面
+  try {
+    const overview = await fetchOverview();
+    for (const p of overview.sidebar_pages ?? []) {
+      entries.push({
+        url: `${baseUrl}/p/${p.slug}`,
+        lastModified: new Date(),
+        changeFrequency: "monthly",
+        priority: 0.4,
+      });
+    }
+  } catch {
+    /* 忽略 */
+  }
+
   return entries;
 }