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/page.tsx

@@ -22,7 +22,6 @@ import PostRow from "@/components/PostRow";
 import FeedTabs from "@/components/home/FeedTabs";
 import FeedNewTip from "@/components/home/FeedNewTip";
 import { WorkspaceNavMobile } from "@/components/home/WorkspaceNav";
-import { SiteDocBreadcrumb } from "@/components/site-doc";
 import { BoardMissingPanel } from "@/components/home/BoardPanels";
 import { requestCanonical } from "@/lib/canonicalMeta";
 import { defaultFeedSort, homeCanonicalQuery, normalizeFeedSort } from "@/lib/siteUrl";
@@ -131,6 +130,13 @@ export default async function HomePage({ searchParams }: HomePageProps) {
 
   // 侧栏布局：板块态右栏走 board 配置（左栏跟随首页），其余走 home 配置
   const scopeLists = sidebarScopeLists(sidebar.config, showBoardPanels ? "board" : "home");
+  // 三栏竖向分隔线跟随左右栏显隐（空配置不画悬空线）
+  const hasLeftRail = scopeLists.left.length > 0;
+  const hasRightRail = showBoardPanels
+    ? boardSidebar
+      ? scopeLists.right.length > 0
+      : boardPanelsMissing
+    : !!(overview && scopeLists.right.length > 0);
   const sidebarProps: SidebarBlockProps = {
     allowComments,
     user,
@@ -202,7 +208,7 @@ export default async function HomePage({ searchParams }: HomePageProps) {
           </h1>
           <p className="meta mt-2">共 {postsData.total} 篇结果 · 按相关度与时间排序</p>
         </div>
-        <div className="panel overflow-hidden">
+        <div className="panel overflow-hidden max-sm:-mx-4 max-sm:rounded-none max-sm:border-x-0 max-sm:shadow-none">
           {postsData.posts.length > 0 ? (
             postsData.posts.map((post, i) => (
               <PostRow key={post.id} post={post} showBoard index={i} showViews={false} showLike={false} />
@@ -231,37 +237,30 @@ export default async function HomePage({ searchParams }: HomePageProps) {
   if (sort !== defaultFeedSort(allowComments)) pageQuery.sort = sort;
 
   return (
-    <div>
+    <div className="j13-fluid-home">
       <JsonLd data={listingLd} />
-      <WorkspaceNavMobile boards={boards} user={user} />
+      <WorkspaceNavMobile boards={boards} />
 
-      <div className={`flex items-start gap-6 xl:gap-7 ${activeBoard ? "" : "mt-5 lg:mt-0"}`}>
+      <div className={`flex items-start gap-6 xl:gap-7 ${activeBoard ? "" : "lg:mt-0"}`}>
         {/* 左栏：按配置渲染（缺省 = 板块目录） */}
         {scopeLists.left.length > 0 && (
-          <aside className="hidden lg:block w-56 xl:w-60 shrink-0 sticky top-[var(--rail-top)] max-h-[var(--rail-max-h)]">
+          <aside className="j13-rail-left hidden lg:block w-56 xl:w-60 shrink-0 sticky top-[var(--rail-top)] max-h-[var(--rail-max-h)]">
             <SidebarRenderer blocks={scopeLists.left} widgets={sidebar.widgets} props={sidebarProps} />
           </aside>
         )}
 
-        {/* 中栏：tab 栏与帖子流为同一个整体卡片（左栏切板块只替换这一列） */}
-        <div className="flex-1 min-w-0">
+        {/* 中栏：tab 栏与帖子流为同一个整体（左栏切板块只替换这一列） */}
+        <div
+          className={`flex-1 min-w-0 ${hasLeftRail ? "j13-home-sep-l" : ""} ${
+            hasRightRail ? "j13-home-sep-r" : ""
+          }`}
+        >
           <h1 className="sr-only">{pageName}</h1>
 
-          <div className="panel overflow-hidden">
-            {activeBoard ? (
-              <div className="px-3 sm:px-4 pt-3">
-                <SiteDocBreadcrumb
-                  className="is-ruled !mb-0"
-                  items={[
-                    { href: "/", label: "首页" },
-                    { label: activeBoard.name },
-                  ]}
-                />
-              </div>
-            ) : null}
-            <div className="flex items-center justify-between gap-2 px-3 sm:px-4 pt-3 pb-2.5">
+          <div className="max-sm:-mx-4">
+            <div className="j13-feed-head flex items-stretch justify-between gap-2 px-3 sm:px-4">
               <FeedTabs current={sort} boardId={boardId} />
-              <span className="meta shrink-0 text-[12px] tabular-nums">
+              <span className="meta self-center shrink-0 text-[12px] tabular-nums">
                 共 {postsData.total} 篇
               </span>
             </div>
@@ -329,12 +328,11 @@ export default async function HomePage({ searchParams }: HomePageProps) {
 
       {/* 窄屏：面板下沉到帖子流之后（右栏列表 + 左栏列表，板块目录除外） */}
       {mobileBlocks.length > 0 && (
-        <div className="mt-6 lg:hidden">
+        <div className="j13-flat-rail mt-3 lg:hidden">
           <SidebarRenderer
             blocks={mobileBlocks}
             widgets={sidebar.widgets}
             props={sidebarProps}
-            className="space-y-4"
           />
         </div>
       )}