feat(home): 替换首页轮播图实现为广告系统驱动

- 移除原有的硬编码轮播图组件和相关样式
- 新增 getAdByCode 方法用于获取广告数据
- 实现解析广告数据的工具函数 parseSlides 和 parsePx
- 集成 useAsyncData 获取 flash 广告数据
- 添加备用图片以确保加载失败时的显示
- 更新页面样式适配新的轮播组件结构

app/components/SiteHeader.vue

@@ -30,10 +30,10 @@
       </div>
     </div>
 
-    <a-affix :offset-top="0">
+    <a-affix :offset-top="0" @change="onAffixChange">
       <div class="navbar">
-        <div class="mx-auto flex max-w-screen-xl items-center justify-between gap-3 px-4">
-          <NuxtLink to="/" class="navbar-brand">
+        <div class="mx-auto flex max-w-screen-xl items-center justify-between gap-20 px-">
+          <NuxtLink v-if="isAffixed" to="/" class="navbar-brand" :class="{ 'navbar-brand-hidden': !isAffixed }">
             <img class="navbar-logo" :src="logoUrl" :alt="siteName" />
             <span class="navbar-brand-name">
               {{ siteName }}
@@ -119,6 +119,7 @@ import { COMPANY } from '@/config/company'
 
 const route = useRoute()
 const open = ref(false)
+const isAffixed = ref(false)
 
 type HeaderNavItem = {
   key: string
@@ -281,6 +282,10 @@ const todayText = computed(() => {
   const pad = (n: number) => String(n).padStart(2, '0')
   return `${d.getFullYear()}年${pad(d.getMonth() + 1)}月${pad(d.getDate())}日 星期${week}`
 })
+
+function onAffixChange(affixed: boolean) {
+  isAffixed.value = affixed
+}
 </script>
 
 <style scoped>
@@ -362,11 +367,19 @@ const todayText = computed(() => {
 .navbar-brand {
   display: inline-flex;
   align-items: center;
-  gap: 10px;
+  gap: 20px;
   height: 48px;
   text-decoration: none;
   color: rgba(255, 255, 255, 0.95);
   font-weight: 700;
+  transition: opacity 0.18s ease, transform 0.18s ease;
+}
+
+.navbar-brand-hidden {
+  opacity: 0;
+  visibility: hidden;
+  pointer-events: none;
+  transform: translateY(-4px);
 }
 
 .navbar-logo {
@@ -392,7 +405,7 @@ const todayText = computed(() => {
 
 .nav {
   display: flex;
-  gap: 2px;
+  gap: 10px;
 }
 
 .nav-link {