feat: 帖子收藏与用户关注

- 新增收藏功能：favorite 服务与 handler、FavoriteButton 组件
- 新增关注功能：follow 服务与 handler、FollowButton 组件
- 用户主页适配关注/粉丝与收藏展示
- flash 消息工具、广告与侧边栏组件微调

frontend/components/TipHost.tsx

@@ -136,7 +136,17 @@ export default function TipHost() {
   const activeEl = useRef<Element | null>(null);
 
   useEffect(() => {
+    let pendingTimer: number | null = null;
+
+    const clearPending = () => {
+      if (pendingTimer !== null) {
+        window.clearTimeout(pendingTimer);
+        pendingTimer = null;
+      }
+    };
+
     const hide = () => {
+      clearPending();
       activeEl.current = null;
       setTip(null);
     };
@@ -160,8 +170,27 @@ export default function TipHost() {
         hide();
         return;
       }
-      activeEl.current = host;
-      placeTip(host, text);
+      // 同一目标已在显示：直接复位位置，不重新计时
+      if (activeEl.current === host && pendingTimer === null) {
+        placeTip(host, text);
+        return;
+      }
+      // data-tip-delay="毫秒"：停留一会再显示，期间移出即取消
+      const delay = Number(host.getAttribute("data-tip-delay") || 0);
+      if (!Number.isFinite(delay) || delay <= 0) {
+        clearPending();
+        activeEl.current = host;
+        placeTip(host, text);
+        return;
+      }
+      clearPending();
+      pendingTimer = window.setTimeout(() => {
+        pendingTimer = null;
+        const focused = host.contains(document.activeElement);
+        if (!host.matches(":hover") && !focused) return;
+        activeEl.current = host;
+        placeTip(host, text);
+      }, delay);
     };
 
     const onOver = (e: Event) => {
@@ -202,6 +231,7 @@ export default function TipHost() {
     window.addEventListener("resize", onScrollOrResize);
 
     return () => {
+      clearPending();
       document.removeEventListener("mouseover", onOver);
       document.removeEventListener("mouseout", onOut);
       document.removeEventListener("focusin", onOver);