feat: 实现主题、黑名单、排程等14项功能迭代

- style(theme): 修复浅色模式不生效问题，为 ClassicLight 和 ModernLight 增加独立差异化 CSS 变量定义（主色/圆角/阴影/背景对比度）
- feat(blacklist): 后端放开 LANGUAGE/GENRE 类型校验；check API 新增语种（CJK/拉丁/假名/谚文/西里尔/阿拉伯）和曲风关键词匹配逻辑；前端 BlacklistManager UI 增加 语种/曲风 四类型切换、类型筛选、图标与标签颜色映射、输入提示
- fix(DataAnalysisPanel): 活跃用户列表容器加 max-h-[400px] + overflow-y-auto + 底部渐变遮罩；tooltip 加 max-height + truncate 防止超高；头像失败回退首字母
- feat(admin): 新增 user-avatar.ts 工具（OAuth→Gravatar→DiceBear 三级兜底）；active-users/realtime/users 列表返回 avatarUrl；DataAnalysisPanel/UserManager 展示圆形头像；权限分级 ROLE_LEVELS，SUPER_ADMIN 全权限，ADMIN 仅可管理 ≤ USER 级用户的密码与角色，前端按钮联动禁用
- fix+style(schedule): ScheduleManager 标签页 sticky min-h 防抖、间距调优、表单分组、移动端 padding 统一
- feat(schedule): 自动排期新增「按投稿人数优先覆盖」策略（算法：requester + collaborators 总数降序），支持 CustomSelect 切换；新增 localStorage voicehub:schedule:auto-config 持久化 7 项配置（策略/时段/年级/排序/标签/搜索/学期）500ms debounce
- fix(schedule): songs/index.get 新增 usePool 参数，从 schedule_song_pool(status=PENDING,targetPlayDate IS NULL) 取歌并去重，排除已排期 songs.played=false；schedule.post 和 draft-bulk 分配后更新池状态为 ASSIGNED 避免重复分配
- feat(player): ScheduleManager 新增「构建播放队列」按钮，按 playDate→时段→sequence 排序后经 useAudioPlayer.playSong 整列载入并 toast 反馈
- fix(db): db.ts 检测 NETLIFY/VERCEL serverless 环境使用最小池 max=1 idle_timeout=1 keep_alive=false，Node Server 保持 max=10
- feat(site-config): site-config.get.ts 与 useSiteConfig.js 导出 statisticsCode 和 statisticsCodeEnabled；index.vue 挂载后解析 HTML 动态重插 script 元素确保第三方统计执行
- fix(schedule-printer): ScheduleItemPrint 封面 aspect-square object-cover；print-fix.css 打印时强制 48px×48px contain、去除圆角阴影
- fix(songRequest): 新增 server/utils/url.ts normalizeCoverUrl（trim/去零宽空格/相对协议补 https/非 http 丢弃/URL.parse 兜底）；request.post/add.post/import.post 三处写入 cover/coverUrl 前统一规范化

app/components/Admin/ScheduleItemPrint.vue

@@ -7,16 +7,16 @@
       </div>
 
       <!-- 歌曲封面 -->
-      <div v-if="settings.showCover" class="cover-section">
+      <div v-if="settings.showCover" class="cover-section aspect-square">
         <img
           v-if="schedule.song.cover"
           :alt="schedule.song.title"
           :src="convertToHttps(schedule.song.cover)"
-          class="song-cover"
+          class="song-cover object-cover"
           referrerpolicy="no-referrer"
           @error="handleImageError"
         >
-        <div class="cover-placeholder" :class="{ 'show': !schedule.song.cover }">
+        <div class="cover-placeholder object-contain" :class="{ 'show': !schedule.song.cover }">
           <svg fill="none" stroke="currentColor" stroke-width="2" viewBox="0 0 24 24">
             <circle cx="12" cy="12" r="3" />
             <path d="M12 1v6m0 6v6" />
@@ -119,6 +119,7 @@ const handleImageError = (event) => {
 .cover-section {
   width: 40px;
   height: 40px;
+  aspect-ratio: 1 / 1;
   flex-shrink: 0;
 }
 
@@ -127,11 +128,14 @@ const handleImageError = (event) => {
   height: 100%;
   object-fit: cover;
   border-radius: 4px;
+  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
 }
 
 .cover-placeholder {
   width: 100%;
   height: 100%;
+  aspect-ratio: 1 / 1;
+  object-fit: contain;
   background: #f5f5f5;
   border-radius: 4px;
   display: none;
@@ -233,11 +237,27 @@ const handleImageError = (event) => {
   }
 
   .cover-section {
-    width: 40px !important;
-    height: 40px !important;
+    width: 48px !important;
+    height: 48px !important;
+    aspect-ratio: 1 / 1 !important;
     flex-shrink: 0 !important;
   }
 
+  .song-cover {
+    width: 100% !important;
+    height: 100% !important;
+    object-fit: contain !important;
+    border-radius: 0 !important;
+    box-shadow: none !important;
+  }
+
+  .cover-placeholder {
+    width: 100% !important;
+    height: 100% !important;
+    object-fit: contain !important;
+    border-radius: 0 !important;
+  }
+
   .song-info {
     flex: 1 !important;
     min-width: 0 !important;