流体交互层：按压反馈 + 真半透明材质 + 主题交叉过渡 + 弹层材质化

按 apple-design（Designing Fluid Interfaces）审查落地：
- 全站补 :active 按压缩放反馈（按钮/tab/链接/命令面板/前后栏导航），交互元素加 touch-action
- TopBar、首页标题栏、浮动主题钮改 color-mix 半透明 + blur 真材质，配 reduced-transparency 回退
- 主题切换 250ms 交叉过渡（theme-anim 瞬时类），消除亮度突变
- CommandPalette/ShortcutsPanel 过 <Transition name="pop">：scrim 淡入 + 面板自顶部锚点 scale 进入，退出原路返回
- 首页标题栏收缩由二值跳变改为滚动进度 --sq 连续插值（16–56px）
- reduced-motion 例外：弹层保留短交叉淡入，禁位移与主题过渡
- 触控目标增大（主题钮 40/44px、tab、后台导航项），文章大标题负字距 + 收紧行高

frontend/src/styles.css

@@ -620,7 +620,7 @@ h4 {
   display: flex;
   align-items: center;
   gap: 10px;
-  padding: 8px 12px;
+  padding: 10px 12px;
   border-radius: 6px;
   font-size: 14px;
   color: var(--admin-ink-soft);
@@ -1825,3 +1825,78 @@ body:not(.admin-shell-active) :where(a, button, input, select, textarea, [tabind
 .cmd-overlay {
   overscroll-behavior: contain;
 }
+
+/* ============================================================
+   流体交互层（apple-design 审查落地）
+   ============================================================ */
+
+/* 按压反馈：从按下瞬间就有反应，而不是 hover 或松手 */
+button:active:not(:disabled),
+a.btn:active,
+a.pill:active,
+.tab:active,
+.tag-chip:active,
+.rail-left .item:active,
+.admin-side .item:active,
+.cmd-panel .row:active {
+  transform: scale(0.97);
+}
+
+/* 触屏：去掉浏览器对双击缩放的猜测延迟 */
+button,
+a.btn,
+a.pill,
+.tab,
+.tag-chip,
+.rail-left .item,
+.admin-side .item {
+  touch-action: manipulation;
+}
+
+/* 主题切换：亮度突变改为一次性的 250ms 交叉过渡（仅切换瞬间挂载） */
+html.theme-anim,
+html.theme-anim * {
+  transition: background-color 250ms ease, color 250ms ease, border-color 250ms ease !important;
+}
+
+/* 弹层材质化：从触发源方向 scale+fade 进入，退出走同一条路径 */
+.cmd-panel {
+  transform-origin: top center;
+}
+.pop-enter-active {
+  transition: opacity 160ms ease-out;
+}
+.pop-enter-active .cmd-panel {
+  transition: transform 240ms cubic-bezier(0.2, 0.8, 0.25, 1), opacity 160ms ease-out;
+}
+.pop-enter-from {
+  opacity: 0;
+}
+.pop-enter-from .cmd-panel {
+  transform: scale(0.96) translateY(-10px);
+  opacity: 0;
+}
+.pop-leave-active {
+  transition: opacity 130ms ease-in;
+}
+.pop-leave-to {
+  opacity: 0;
+}
+
+/* reduce ≠ 无反馈：保留短交叉淡入，去掉位移/缩放与主题过渡 */
+@media (prefers-reduced-motion: reduce) {
+  .pop-enter-active,
+  .pop-leave-active {
+    transition: opacity 150ms ease !important;
+  }
+  .pop-enter-active .cmd-panel {
+    transition: opacity 150ms ease !important;
+  }
+  .pop-enter-from .cmd-panel {
+    transform: none;
+  }
+  html.theme-anim,
+  html.theme-anim * {
+    transition: none !important;
+  }
+}