feat: 云盘/下载音乐分离/粘性头部/播放状态同步/歌手关注

新增:
- 音乐云盘页面(列表/详情弹窗/删除/存储空间, NOS multipart上传+LBS区域查询+进度事件)
- 下载音乐页面(独立于本地音乐, 只显示应用下载的歌曲)
- PageHeader粘性头部组件(IntersectionObserver控制显隐, 渐变模糊背景)
- useLocalMusic composable(LocalSong类型/formatFileSize/localSongToSong/fetchMissingCovers)
- 云盘上传完整流程(cloud_upload命令: check->token->LBS->NOS分块上传->info->publish)
- 云盘API(user_cloud/user_cloud_detail/user_cloud_del)
- 歌手关注/取关(artist_sub/artist_sublist命令, ArtistDetail关注按钮+artistSublist查询状态)
- 本地音乐多文件夹扫描(scan_local_folders命令, settings.localMusicPaths, 模态框管理)
- 侧边栏下载音乐和云盘导航项, 路由新增downloaded-music和cloud-music
- md5 crate依赖

改进:
- 路由全部改为懒加载
- keep-alive缓存管理重写(30s TTL+导航栈保护+FavoriteSongs常驻+10s定时清理)
- 播放器状态同步改为轮询isAudioPlaying(替代audio-started事件), 超时后watchForLatePlayback继续监听
- audio.rs新增is_playing原子状态+is_audio_playing命令
- 同步命令改async+spawn_blocking(list_local_songs/delete_local_song/check_local_song/get_default_download_path)
- scan_dir_for_songs抽取为公共函数, 新增downloaded_only参数
- RoamDrawer tab状态从组件本地ref移至store(roamTab替换roamInitialTab)
- App.vue onMounted改为非阻塞
- 多页面添加骨架屏加载态和加载失败重试
- 多页面使用PageHeader替代手动返回按钮
- PlaylistDetail/ArtistDetail添加简介弹窗(溢出时显示查看完整介绍)
- Home推荐/排行榜拆分为独立fetch函数支持分别重试
- Toast去重(3s窗口)+数量限制(最多3条)
- LocalMusic移除删除功能改文件夹模态框, ArtistDetail头像改圆形简介内嵌
- README重写

修复:
- 播放超时后后端实际开始播放但UI显示暂停(watchForLatePlayback+tick定期同步isAudioPlaying)
- FM播放缺少playSeq竞态保护
- scrobble离线时仍发送(添加navigator.onLine检查)
- RoamDrawer已打开时点击评论按钮无法切换(roamTab移至store)
- 关闭RoamDrawer后再打开永远显示评论(closeRoamDrawer重置roamTab)
- 歌手详情页关注状态离开后丢失(artist_detail不返回followed, 改用artistSublist查询)
- audio-ended事件在切歌时误触发(新增_switchingSong标志拦截)
- 路由beforeEach中localStorage key从user改为user_profile
- toggle播放前先同步后端状态

src/components/RoamDrawer.vue

@@ -43,18 +43,18 @@
         </div>
         <div class="w-3/5 relative min-h-0 overflow-hidden flex flex-col">
           <div class="flex items-center gap-1 mb-3 px-4">
-            <button @click="roamTab = 'lyric'"
+            <button @click="player.roamTab = 'lyric'"
               class="px-3 py-1 rounded-full text-sm transition"
               :class="player.dominantColor
-                ? (roamTab === 'lyric' ? 'bg-white/15 text-white font-medium' : 'text-white/50 hover:text-white/80')
-                : (roamTab === 'lyric' ? 'bg-muted text-content font-medium' : 'text-content-3 hover:text-content')">
+                ? (player.roamTab === 'lyric' ? 'bg-white/15 text-white font-medium' : 'text-white/50 hover:text-white/80')
+                : (player.roamTab === 'lyric' ? 'bg-muted text-content font-medium' : 'text-content-3 hover:text-content')">
               歌词
             </button>
-            <button @click="roamTab = 'comment'"
+            <button @click="player.roamTab = 'comment'"
               class="px-3 py-1 rounded-full text-sm transition"
               :class="player.dominantColor
-                ? (roamTab === 'comment' ? 'bg-white/15 text-white font-medium' : 'text-white/50 hover:text-white/80')
-                : (roamTab === 'comment' ? 'bg-muted text-content font-medium' : 'text-content-3 hover:text-content')">
+                ? (player.roamTab === 'comment' ? 'bg-white/15 text-white font-medium' : 'text-white/50 hover:text-white/80')
+                : (player.roamTab === 'comment' ? 'bg-muted text-content font-medium' : 'text-content-3 hover:text-content')">
               评论
             </button>
             <button v-if="hasTranslation" @click="toggleTranslation"
@@ -66,7 +66,7 @@
               译
             </button>
           </div>
-          <div v-show="roamTab === 'lyric'" ref="lyricScrollContainer" class="flex-1 min-h-0 overflow-y-auto custom-scroll px-4">
+          <div v-show="player.roamTab === 'lyric'" ref="lyricScrollContainer" class="flex-1 min-h-0 overflow-y-auto custom-scroll px-4">
             <div v-if="lyrics.length > 0" class="w-full max-w-lg mx-auto text-center"
               :style="{ paddingTop: roamLyricPadPx + 'px', paddingBottom: roamLyricPadPx + 'px' }">
               <p
@@ -84,7 +84,7 @@
             </div>
             <div v-else :class="player.dominantColor ? 'text-white/40' : 'text-content-3'" class="text-center mt-8">暂无歌词</div>
           </div>
-          <div v-show="roamTab === 'comment'" class="flex-1 min-h-0 overflow-y-auto px-4 pb-4">
+          <div v-show="player.roamTab === 'comment'" class="flex-1 min-h-0 overflow-y-auto px-4 pb-4">
             <CommentSection v-if="roamSong" :type="0" :id="player.commentSongId || roamSong.id" :key="player.commentSongId || roamSong.id" :dark-mode="!!player.dominantColor" />
           </div>
         </div>
@@ -118,7 +118,6 @@ const roamLyricHovering = ref(false);
 const roamLyricPadPx = ref(0);
 const roamSong = computed(() => player.currentSong);
 const roamCoverError = ref(false);
-const roamTab = ref<'lyric' | 'comment'>('lyric');
 const roamCoverUrl = computed(() => {
   if (!roamSong.value) return '';
   return getCoverUrl(roamSong.value) || '';
@@ -144,7 +143,6 @@ function updateRoamLyricPad() {
 
 watch(() => player.showRoamDrawer, (val) => {
   if (val) {
-    roamTab.value = player.roamInitialTab;
     nextTick(() => {
       updateRoamLyricPad();
       if (roamResizeObserver) roamResizeObserver.disconnect();