feat: v0.3.0 - 流式播放、本地音乐、下载系统、漫游修复

### 新功能
- 流式播放：边下载边播放，缓冲 64KB 后即刻开始，无需等待完整下载
- 本地音乐页面：支持浏览、播放本地歌曲，横向菜单含「从磁盘删除」
- 下载系统：支持下载歌曲到自定义路径，保存完整元数据（封面/专辑/时长）
- 封面补全：本地音乐缺少封面时自动从网易云 API 获取
- 更新信息：接入 Gitea Releases API，查看最新版更新日志

### 修复
- 修复私人漫游播完一首歌后跳三首的问题（双重触发：audio-ended + startTick）
- 修复全屏漫游抽屉和漫游页面无封面歌曲显示破损图片
- 修复 PlayerBar 无封面歌曲显示破损图片
- 修复下载路径修改后不生效（Rust serde camelCase 映射）
- 修复本地音乐始终只显示默认路径歌曲
- 修复下载完成提示弹出 4 次
- 修复播放网络歌曲时进度条先走但无声音（audio-started 事件同步）

### 优化
- PlayerBar 下载状态：未下载显示下载按钮，下载中显示进度，已下载不显示
- audio.rs 新增 manual_stop 标志防止 stop_audio 触发虚假 audio-ended
- player.ts 新增 waitForAudioStart() 确保 playing 状态与实际播放同步
- 切歌/停止时立即清除 tickInterval 防止重复触发 next()

src/composables/useDownload.ts

@@ -0,0 +1,135 @@
+import { reactive, watch } from 'vue';
+import { invoke } from '@tauri-apps/api/core';
+import { listen } from '@tauri-apps/api/event';
+import { useSettingsStore } from '../stores/settings';
+import { showToast } from '../composables/useToast';
+
+interface DownloadTask {
+  id: number;
+  name: string;
+  progress: number;
+}
+
+const downloadingIds = reactive<Set<number>>(new Set());
+const tasks = reactive<DownloadTask[]>([]);
+const localSongIds = reactive<Set<number>>(new Set());
+
+let listenerSetup = false;
+let storeSetup = false;
+
+async function setupDownloadListener() {
+  if (listenerSetup) return;
+  listenerSetup = true;
+  await listen<{ id: number; progress: number; name: string }>('download-progress', (event) => {
+    const { id, progress, name } = event.payload;
+    if (progress >= 100) {
+      const idx = tasks.findIndex(t => t.id === id);
+      if (idx >= 0) {
+        tasks.splice(idx, 1);
+        downloadingIds.delete(id);
+        showToast(`${name} 下载完成`, 'success');
+      }
+    } else {
+      const task = tasks.find(t => t.id === id);
+      if (task) {
+        task.progress = progress;
+      }
+    }
+  });
+}
+
+async function refreshLocalIds() {
+  try {
+    const settings = useSettingsStore();
+    const list: { id: number }[] = await invoke('list_local_songs', { downloadPath: settings.downloadPath || null });
+    localSongIds.clear();
+    for (const s of list) {
+      localSongIds.add(s.id);
+    }
+  } catch {}
+}
+
+function ensureStoreSetup() {
+  if (storeSetup) return;
+  storeSetup = true;
+  const settings = useSettingsStore();
+  refreshLocalIds();
+  watch(() => settings.downloadPath, () => {
+    refreshLocalIds();
+  });
+}
+
+function isDownloaded(songId: number): boolean {
+  return localSongIds.has(songId);
+}
+
+function isDownloading(songId: number): boolean {
+  return downloadingIds.has(songId);
+}
+
+function getDownloadProgress(songId: number): number {
+  const task = tasks.find(t => t.id === songId);
+  return task?.progress ?? 0;
+}
+
+async function downloadSong(song: { id: number; name: string; ar?: { name: string }[]; artists?: { name: string }[]; al?: { picUrl?: string; name?: string }; album?: { picUrl?: string; name?: string }; dt?: number; duration?: number }) {
+  if (downloadingIds.has(song.id)) return;
+  if (localSongIds.has(song.id)) {
+    showToast(`${song.name} 已下载`, 'info');
+    return;
+  }
+
+  const settings = useSettingsStore();
+  const artist = song.ar?.map(a => a.name).join(' / ') || song.artists?.map(a => a.name).join(' / ') || '未知';
+  const albumName = song.al?.name || song.album?.name || null;
+  const durationVal = song.dt || song.duration || null;
+  const coverUrl = song.al?.picUrl || song.album?.picUrl || null;
+
+  downloadingIds.add(song.id);
+  tasks.push({ id: song.id, name: song.name, progress: 0 });
+
+  try {
+    await invoke('download_song', {
+      query: {
+        id: song.id,
+        name: song.name,
+        artist,
+        album: albumName,
+        duration: durationVal,
+        coverUrl,
+        level: settings.audioQuality,
+        downloadPath: settings.downloadPath || null,
+      },
+    });
+    localSongIds.add(song.id);
+  } catch (e: any) {
+    downloadingIds.delete(song.id);
+    const idx = tasks.findIndex(t => t.id === song.id);
+    if (idx >= 0) tasks.splice(idx, 1);
+    if (e === '文件已存在') {
+      localSongIds.add(song.id);
+      showToast(`${song.name} 已下载`, 'info');
+    } else if (e === 'VIP歌曲无法下载') {
+      showToast(`${song.name} 为 VIP 歌曲，无法下载`, 'error');
+    } else if (typeof e === 'string' && e.includes('VIP')) {
+      showToast(`${song.name} 需要 VIP 权限才能下载`, 'error');
+    } else {
+      showToast(`下载失败: ${e}`, 'error');
+    }
+  }
+}
+
+export function useDownload() {
+  setupDownloadListener();
+  ensureStoreSetup();
+  return {
+    downloadingIds,
+    tasks,
+    localSongIds,
+    isDownloaded,
+    isDownloading,
+    getDownloadProgress,
+    downloadSong,
+    refreshLocalIds,
+  };
+}