feat: 新增站点公告系统与多项体验优化

此提交完成了以下核心功能与优化：
1. 新增站点公告全流程支持：包含公告模型、CRUD接口、管理后台页面、公告详情页与首页展示
2. 实现评论楼层化与回复嵌套：重构评论系统为树状结构，支持回复评论与层级限制
3. 添加用户在线状态追踪：异步更新用户最后活跃时间并做SQL限频
4. 优化用户体验：移动端浮动操作条、统一板块标签样式、用户页签到积分展示、注册即登录优化
5. 其他细节优化：SEO站点地图新增公告页、评论分页与统计、登录/注册表单增强等

frontend/app/post/[id]/page.tsx

@@ -23,16 +23,20 @@ import {
   type Board,
 } from "@/lib/api";
 import { authCookieHeader } from "@/lib/cookies";
+import { getMeCached } from "@/lib/serverData";
 import CommentSection from "@/components/CommentSection";
 import PostActions from "@/components/PostActions";
 import LikeButton from "@/components/LikeButton";
 import ReadingProgress from "@/components/ReadingProgress";
 import PostToc, { type TocItem } from "@/components/PostToc";
+import MobilePostBar from "@/components/MobilePostBar";
 import Avatar from "@/components/Avatar";
 import { IconComment, IconEye } from "@/components/Icons";
 
 interface PageProps {
   params: Promise<{ id: string }>;
+  // page 同时用于评论分页（?page=N），帖子正文本身不分页
+  searchParams: Promise<{ page?: string }>;
 }
 
 export async function generateMetadata({ params }: PageProps): Promise<Metadata> {
@@ -313,14 +317,17 @@ function AuthorCardStacked({ profile }: { profile: UserProfile }) {
   );
 }
 
-export default async function PostDetailPage({ params }: PageProps) {
+export default async function PostDetailPage({ params, searchParams }: PageProps) {
   const { id } = await params;
+  const sp = await searchParams;
+  const commentPage = Math.max(1, parseInt(sp.page || "1", 10) || 1);
   const cookie = authCookieHeader(await cookies());
   const { post } = await fetchPostDetail(id, cookie);
 
-  // 评论 / 作者资料 / 同板块热议并行拉取；侧栏数据失败一律静默降级，不阻塞正文
-  const [commentsData, profile, relatedData] = await Promise.all([
-    fetchComments(id),
+  // 评论 / 当前用户 / 作者资料 / 同板块热议并行拉取；侧栏数据失败一律静默降级，不阻塞正文
+  const [commentsData, me, profile, relatedData] = await Promise.all([
+    fetchComments(id, commentPage),
+    getMeCached(cookie || undefined),
     fetchUserProfile(String(post.user.id), 1, cookie).catch(() => null),
     fetchPosts(1, 8, post.board_id, "hot", "", false, cookie).catch(() => null),
   ]);
@@ -369,6 +376,8 @@ export default async function PostDetailPage({ params }: PageProps) {
     <>
       <ReadingProgress />
       <script type="application/ld+json" dangerouslySetInnerHTML={{ __html: JSON.stringify(jsonLd) }} />
+      {/* 移动端浮动操作条：长文阅读中途可点赞 / 跳评论 / 回顶部 */}
+      <MobilePostBar postId={id} liked={post.liked} likeCount={post.like_count} />
 
       {/* 三栏阅读布局：xl = 左导航240 + 正文 + 右辅助280；lg = 正文 + 右辅助260；以下单栏 */}
       <div className="grid grid-cols-1 items-start lg:grid-cols-[minmax(0,1fr)_260px] xl:grid-cols-[240px_minmax(0,1fr)_280px] gap-x-6 xl:gap-x-7">
@@ -487,7 +496,15 @@ export default async function PostDetailPage({ params }: PageProps) {
               </div>
             )}
 
-            <CommentSection postId={id} comments={comments} />
+            <CommentSection
+              postId={id}
+              comments={comments}
+              total={commentsData.total}
+              totalComments={commentsData.total_comments}
+              page={commentsData.page}
+              size={commentsData.size}
+              user={me.user}
+            />
 
             {/* 窄屏相关讨论（lg 起由右栏承载） */}
             <div className="lg:hidden mt-6">
@@ -505,6 +522,9 @@ export default async function PostDetailPage({ params }: PageProps) {
           <RelatedPosts posts={related} boardId={post.board_id} />
         </aside>
       </div>
+
+      {/* 给移动端浮动操作条让位，避免遮住页尾内容 */}
+      <div className="lg:hidden h-16" aria-hidden />
     </>
   );
 }