feat(admin): 后台改为左侧导航 + 右侧内容

- 原来的横向 Tabs 换成库里的 Menu，左侧固定导航、右侧面板
- 首页管理收成一组：侧边栏 / 内容卡片 / 页头 三个子项，页头从顶层移入
- 页头、资料仍需手动保存，保存/撤销按钮留在各自面板底部
- 窄屏（<=860px）导航折到内容上方
- 后台内容区宽度不变（1340），导航列 190px + 24px 间距

stash-web/src/App.css

@@ -53,6 +53,40 @@
   padding: 0 var(--su-space-5);
 }
 
+/* 后台：左侧导航 + 右侧内容 */
+.admin-shell {
+  display: grid;
+  grid-template-columns: 190px minmax(0, 1fr);
+  gap: var(--su-space-6);
+  align-items: start;
+  margin-top: var(--su-space-5);
+}
+
+.admin-nav {
+  position: sticky;
+  top: calc(var(--su-header-height) + var(--su-space-5));
+  padding-right: var(--su-space-4);
+  border-right: 1px solid var(--su-border);
+}
+
+.admin-panel {
+  min-width: 0;
+}
+
+@media (max-width: 860px) {
+  .admin-shell {
+    grid-template-columns: 1fr;
+  }
+
+  .admin-nav {
+    position: static;
+    padding-right: 0;
+    border-right: none;
+    border-bottom: 1px solid var(--su-border);
+    padding-bottom: var(--su-space-3);
+  }
+}
+
 /* 后台「首页 Logo」的实时预览：外观交给库里的 Brand，这里只管外框 */
 .brand-preview {
   display: flex;

stash-web/src/components/admin/AdminNext.tsx

@@ -7,13 +7,13 @@ import {
   ICON_NAMES,
   IconButton,
   Input,
+  Menu,
   Modal,
   Notice,
   PasswordInput,
   Select,
   Space,
   Switch,
-  Tabs,
   Tag,
   Text,
   Textarea,
@@ -21,6 +21,7 @@ import {
   Toaster,
   toast,
   type IconName,
+  type MenuItem,
 } from '@stash/ui'
 import { useEffect, useMemo, useRef, useState } from 'react'
 import { changePassword, fetchSession, logout, type SessionState } from '../../auth'
@@ -63,7 +64,31 @@ import type { Project } from '../../api'
  * - 内容是条目，挂在分组上；
  * - 侧边栏、首页卡片都只是「勾选分组」的展示组合。
  */
-type TabKey = 'groups' | 'content' | 'home' | 'header' | 'profile' | 'system'
+type TabKey =
+  | 'groups'
+  | 'content'
+  | 'home-sidebar'
+  | 'home-cards'
+  | 'home-header'
+  | 'profile'
+  | 'system'
+
+/** 左侧导航：首页管理下面挂三个子项，页头也归到这一组 */
+const ADMIN_NAV: MenuItem[] = [
+  { key: 'groups', label: '分组管理' },
+  { key: 'content', label: '数据管理' },
+  {
+    key: 'home',
+    label: '首页管理',
+    children: [
+      { key: 'home-sidebar', label: '侧边栏' },
+      { key: 'home-cards', label: '内容卡片' },
+      { key: 'home-header', label: '页头' },
+    ],
+  },
+  { key: 'profile', label: '资料' },
+  { key: 'system', label: '系统' },
+]
 
 const FORMAT_OPTIONS = [
   { value: 'apps', label: '应用' },
@@ -276,33 +301,28 @@ export function AdminNext() {
           )}
 
           {authenticated && draft !== null && (
-            <>
-              <Tabs
-                className="admin-tabs"
-                items={[
-                  { key: 'groups', label: '分组管理' },
-                  { key: 'content', label: '数据管理' },
-                  { key: 'home', label: '首页管理' },
-                  { key: 'header', label: '页头' },
-                  { key: 'profile', label: '资料' },
-                  { key: 'system', label: '系统' },
-                ]}
-                activeKey={tab}
-                onChange={(key) => setTab(key as TabKey)}
-              />
-
-              {tab === 'groups' && (
-                <GroupsPanel
-                  groups={groups}
-                  onReload={load}
-                  onDelete={(key, title) => setPending({ kind: 'group', id: key, title })}
+            <div className="admin-shell">
+              <nav className="admin-nav">
+                <Menu
+                  items={ADMIN_NAV}
+                  activeKey={tab}
+                  onSelect={(key) => setTab(key as TabKey)}
+                  itemHeight={40}
                 />
-              )}
+              </nav>
 
-              {tab === 'content' && <ContentPanel groups={groups} onReload={load} />}
+              <div className="admin-panel">
+                {tab === 'groups' && (
+                  <GroupsPanel
+                    groups={groups}
+                    onReload={load}
+                    onDelete={(key, title) => setPending({ kind: 'group', id: key, title })}
+                  />
+                )}
 
-              {tab === 'home' && (
-                <div className="admin-home">
+                {tab === 'content' && <ContentPanel groups={groups} onReload={load} />}
+
+                {tab === 'home-sidebar' && (
                   <section className="admin-home-section">
                     <Title level={4}>侧边栏</Title>
                     <SidebarPanel
@@ -320,9 +340,9 @@ export function AdminNext() {
                       }}
                     />
                   </section>
+                )}
 
-                  <div className="sidebar-divider" />
-
+                {tab === 'home-cards' && (
                   <section className="admin-home-section">
                     <Title level={4}>内容卡片</Title>
                     <Text size="sm" tone="muted">
@@ -337,44 +357,44 @@ export function AdminNext() {
                       onDelete={(id, title) => setPending({ kind: 'card', id: String(id), title })}
                     />
                   </section>
-                </div>
-              )}
+                )}
 
-              {tab === 'header' && (
-                <HeaderPanel
-                  value={draft.header}
-                  onChange={(header) => setDraft({ ...draft, header })}
-                  site={draft.site}
-                  onChangeSite={(site) => setDraft({ ...draft, site })}
-                />
-              )}
+                {tab === 'home-header' && (
+                  <HeaderPanel
+                    value={draft.header}
+                    onChange={(header) => setDraft({ ...draft, header })}
+                    site={draft.site}
+                    onChangeSite={(site) => setDraft({ ...draft, site })}
+                  />
+                )}
 
-              {tab === 'profile' && (
-                <ProfilePanel
-                  value={draft.profile}
-                  onChange={(profile) => setDraft({ ...draft, profile })}
-                />
-              )}
+                {tab === 'profile' && (
+                  <ProfilePanel
+                    value={draft.profile}
+                    onChange={(profile) => setDraft({ ...draft, profile })}
+                  />
+                )}
 
-              {tab === 'system' && <SystemPanel />}
+                {tab === 'system' && <SystemPanel />}
 
-              {(tab === 'header' || tab === 'profile') && (
-                <Space gap="sm" justify="end" className="admin-actions">
-                  <Button
-                    variant="secondary"
-                    onClick={() => {
-                      setDraft(clone(draft))
-                      void load()
-                    }}
-                  >
-                    撤销改动
-                  </Button>
-                  <Button loading={saving} icon={<Icon name="check_line" />} onClick={save}>
-                    保存
-                  </Button>
-                </Space>
-              )}
-            </>
+                {(tab === 'home-header' || tab === 'profile') && (
+                  <Space gap="sm" justify="end" className="admin-actions">
+                    <Button
+                      variant="secondary"
+                      onClick={() => {
+                        setDraft(clone(draft))
+                        void load()
+                      }}
+                    >
+                      撤销改动
+                    </Button>
+                    <Button loading={saving} icon={<Icon name="check_line" />} onClick={save}>
+                      保存
+                    </Button>
+                  </Space>
+                )}
+              </div>
+            </div>
           )}
         </Card>
       </main>