feat(wrapped-ui): 新增 Win98 主题与桌面化外观

- 主题系统新增 win98（显示名 Windows 98，快捷键扩展到 F1-F4），并区分 retro(pixel/CRT) 与桌面 GUI 主题
- 年度总结页新增 Win98 桌面背景与底部任务栏（背景色/视口高度适配）
- 封面与卡片 slide 形态支持 Win98 窗口外观（title bar/icon/controls）
- 主题切换器补充 Win98 选项并新增 Win98 专属切换器
- 新增 Win98 图标资源（Start + 桌面图标）

frontend/components/wrapped/shared/WrappedDeckBackground.vue

@@ -1,6 +1,6 @@
 <template>
   <!-- Shared backdrop for all "Wrapped" slides (keeps cover + cards visually consistent). -->
-  <div class="absolute inset-0 pointer-events-none select-none z-0" aria-hidden="true">
+  <div v-if="theme !== 'win98'" class="absolute inset-0 pointer-events-none select-none z-0" aria-hidden="true">
     <!-- Soft color blobs (brand + warm highlights) -->
     <div class="absolute -top-24 -left-24 w-80 h-80 bg-[#07C160] opacity-[0.08] rounded-full blur-3xl"></div>
     <div class="absolute -top-24 -right-24 w-96 h-96 bg-[#F2AA00] opacity-[0.06] rounded-full blur-3xl"></div>
@@ -18,5 +18,61 @@
     <div class="absolute inset-x-0 top-0 h-40 bg-gradient-to-b from-white/50 to-transparent"></div>
     <div class="absolute inset-x-0 bottom-0 h-44 bg-gradient-to-t from-white/40 to-transparent"></div>
   </div>
+
+  <!-- Win98: classic desktop icons (purely decorative) -->
+  <div v-else class="absolute inset-0 pointer-events-none select-none z-0" aria-hidden="true">
+    <div class="win98-desktop-icons">
+      <div v-for="it in desktopIcons" :key="it.label" class="win98-desktop-icon">
+        <img class="win98-desktop-icon__img" :src="it.src" :alt="it.label" />
+        <div class="win98-desktop-icon__label">{{ it.label }}</div>
+      </div>
+    </div>
+  </div>
 </template>
 
+<script setup>
+const { theme } = useWrappedTheme()
+
+const desktopIcons = [
+  { label: '我的文档', src: '/assets/images/win98-icons/folder.png' },
+  { label: '图片', src: '/assets/images/win98-icons/photos.png' },
+  { label: '收件箱', src: '/assets/images/win98-icons/mail.png' },
+  { label: '回收站', src: '/assets/images/win98-icons/recycle.png' }
+]
+</script>
+
+<style scoped>
+.win98-desktop-icons {
+  position: absolute;
+  top: 84px; /* leave space for top-left controls */
+  left: 14px;
+  display: flex;
+  flex-direction: column;
+  gap: 18px;
+}
+
+.win98-desktop-icon {
+  width: 74px;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 6px;
+}
+
+.win98-desktop-icon__img {
+  width: 32px;
+  height: 32px;
+  image-rendering: pixelated;
+}
+
+.win98-desktop-icon__label {
+  max-width: 74px;
+  padding: 0 2px;
+  font-size: 12px;
+  line-height: 1.1;
+  color: #ffffff;
+  text-align: center;
+  text-shadow: 1px 1px 0 #000000;
+  word-break: break-word;
+}
+</style>