feat: 后台页头加明暗切换；内容卡改用库里的 EntryRow / EntryTile

- 后台页头新增月亮/太阳按钮：写回 site.theme 并即时切换，前后台一起变，
  忽略未登录与保存中
- AppCard -> EntryRow，CesCard -> EntryTile（PosterCard 本来就用 Cover）
- 删除 .app-card / .app-card-* / .ces-card / .ces-body* 手写样式，
  两套卡片的点击语义与悬停反馈统一由库提供

视觉变化：头像认证勾回到库默认尺寸（20px，之前应用里压到 10px）

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

@@ -178,6 +178,28 @@ export function AdminNext() {
     toast.success('侧边栏已保存')
   }
 
+  /** 页头的明暗切换：写回 site.theme，前后台一起变 */
+  const themeSetting = draft?.site.theme ?? document?.settings.site.theme ?? 'auto'
+  const prefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches
+  const isDark = themeSetting === 'dark' || (themeSetting === 'auto' && prefersDark)
+
+  const toggleTheme = async () => {
+    if (document === null || draft === null) return
+    const next = isDark ? 'light' : 'dark'
+    setSaving(true)
+    const result = await saveSettings(document.version, {
+      ...draft,
+      site: { ...draft.site, theme: next },
+    })
+    setSaving(false)
+    if (!result.ok) {
+      toast.error(result.error)
+      return
+    }
+    setDocument(result.document)
+    setDraft(clone(result.document.settings))
+  }
+
   const confirmDelete = async () => {
     if (pending === null) return
     setDeleting(true)
@@ -209,6 +231,12 @@ export function AdminNext() {
           <Brand href="/" name={brandName} mark={brandMark} logo={brandLogo} />
 
           <div className="header-actions">
+            <IconButton
+              label={isDark ? '切换到浅色' : '切换到深色'}
+              icon={<Icon name={isDark ? 'sun_line' : 'moon_line'} />}
+              onClick={() => void toggleTheme()}
+              disabled={!authenticated || saving}
+            />
             <IconButton
               label="返回首页"
               icon={<Icon name="arrow_left_line" />}