feat: 站点媒体库与移动端底部导航，服务测试补强

- 新增媒体库：media_library/media_thumbs 服务（WebP 缩略图）、管理端 media 页面
- 移动端底部导航 MobileTabBar 替换 MobilePostBar
- 旧数据导入增强与测试、路由与登录会话/板块侧边栏测试补强
- site-doc 组件精简（移除 Breadcrumb），文档新增迁移公告说明

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

@@ -29,8 +29,6 @@ import CommentSection from "@/components/CommentSection";
 import PostActions from "@/components/PostActions";
 import LikeButton from "@/components/LikeButton";
 import FavoriteButton from "@/components/FavoriteButton";
-import { SiteDocBreadcrumb } from "@/components/site-doc";
-import MobilePostBar from "@/components/MobilePostBar";
 import Avatar from "@/components/Avatar";
 import RoleBadge from "@/components/RoleBadge";
 import LevelBadge from "@/components/LevelBadge";
@@ -119,7 +117,10 @@ function RelatedPosts({
   if (posts.length === 0) return null;
   const titleId = `${uid}-title`;
   return (
-    <section className="j13-module shrink-0" aria-labelledby={titleId}>
+    <section
+      className="j13-module shrink-0 max-sm:-mx-4 max-sm:rounded-none max-sm:border-x-0 max-sm:shadow-none"
+      aria-labelledby={titleId}
+    >
       <p className="j13-module-title mb-1.5" id={titleId}>
         <Flame size={15} style={{ color: "var(--clay)" }} /> 同板块热议
       </p>
@@ -175,7 +176,7 @@ function AuthorCardStacked({
   const signature = (u.signature || "").trim();
   const { post_count, comment_count, points, streak } = profile.stats;
   return (
-    <div className="panel p-5 sm:p-6">
+    <div className="panel p-4 sm:p-6 max-sm:-mx-4 max-sm:rounded-none max-sm:border-x-0 max-sm:shadow-none">
       <p
         className="text-[11.5px] font-medium tracking-[0.08em] uppercase mb-3.5"
         style={{ color: "var(--ink-3)" }}
@@ -477,15 +478,6 @@ export default async function PostDetailPage({ params, searchParams }: PageProps
   return (
     <>
       <JsonLd data={jsonLd} />
-      {/* 移动端浮动操作条：长文读到中途可点赞 / 跳评论框 */}
-      <MobilePostBar
-        postId={id}
-        liked={post.liked}
-        likeCount={post.like_count}
-        favorited={post.favorited === true}
-        allowComments={allowComments}
-      />
-
       {/* 三栏阅读布局：宽度与首页工作台一致——lg = 左224 + 正文 + 右280，xl = 左240 + 正文 + 右300；以下单栏
           侧栏两列均可被站长清空，网格随之退化为两栏/单栏 */}
       <div
@@ -506,15 +498,8 @@ export default async function PostDetailPage({ params, searchParams }: PageProps
         {/* 中栏：正文主体 */}
         <div className="min-w-0">
           <article className="w-full">
-            <div className="panel p-6 sm:p-8">
-              <SiteDocBreadcrumb
-                className="is-ruled"
-                items={[
-                  { href: "/", label: "首页" },
-                  { href: `/?board=${post.board.id}`, label: post.board.name },
-                ]}
-              />
-              <header className="mb-7">
+            <div className="panel p-4 sm:p-6 lg:p-8 max-sm:-mx-4 max-sm:rounded-none max-sm:border-x-0 max-sm:shadow-none">
+                <header className="mb-5 sm:mb-7">
                 <div className="flex items-start gap-2 flex-wrap mb-6">
                   {/* 仅置顶/推荐在标题左侧 */}
                   {post.pinned > 0 && <span className="badge-pin shrink-0 mt-2 sm:mt-3">置顶</span>}
@@ -690,7 +675,7 @@ export default async function PostDetailPage({ params, searchParams }: PageProps
 
               {/* 文末点赞/收藏：分隔线后居中，唯一的互动入口（作者行不再放置） */}
               <div
-                className="mt-9 pt-7 flex justify-center gap-3"
+                className="mt-6 pt-5 sm:mt-9 sm:pt-7 flex justify-center gap-3"
                 style={{ borderTop: "1px solid var(--line)" }}
               >
                 <LikeButton
@@ -705,7 +690,7 @@ export default async function PostDetailPage({ params, searchParams }: PageProps
 
             {/* 窄屏作者卡（lg 起由左栏承载，避免重复展示） */}
             {profile && (
-              <div className="lg:hidden mt-6">
+              <div className="lg:hidden mt-4">
                 <AuthorCardStacked
                   profile={profile}
                   allowComments={allowComments}
@@ -745,7 +730,10 @@ export default async function PostDetailPage({ params, searchParams }: PageProps
                 }
               />
             ) : allowComments ? (
-              <section className="panel p-6 sm:p-8 mt-6 text-center" aria-label="评论区">
+              <section
+                className="panel p-4 sm:p-6 lg:p-8 mt-4 text-center max-sm:-mx-4 max-sm:rounded-none max-sm:border-x-0 max-sm:shadow-none"
+                aria-label="评论区"
+              >
                 <p className="text-[14px]" style={{ color: "var(--ink-2)" }}>
                   {post.status === "pending" ? "帖子审核通过后开放评论" : "帖子未通过审核，评论已关闭"}
                 </p>
@@ -760,7 +748,7 @@ export default async function PostDetailPage({ params, searchParams }: PageProps
             ) : null}
 
             {/* 窄屏相关讨论（lg 起由右栏承载） */}
-            <div className="lg:hidden mt-6">
+            <div className="lg:hidden mt-4">
               <RelatedPosts
                 posts={related}
                 boardId={post.board_id}
@@ -782,9 +770,6 @@ export default async function PostDetailPage({ params, searchParams }: PageProps
           </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 />
     </>
   );
 }