refactor(download): 重构下载系统，支持暂停/恢复/取消，修复歌词加载

- 新建 DownloadManager 类（主进程），每个任务独立 AbortController 控制
- 新建 Pinia useDownloadStore 作为渲染进程单一数据源
- 支持暂停/恢复/取消下载，支持断点续传（Range header）
- 批量下载全部完成后发送汇总系统通知，单首不重复通知
- 并发数可配置（1-5），队列持久化（重启后恢复）
- 修复下载列表不全、封面加载失败、通知重复等 bug
- 修复本地/下载歌曲歌词加载：优先从 ID3/FLAC 元数据提取，API 作为 fallback
- 删除 useDownloadStatus.ts，统一状态管理
- DownloadDrawer/DownloadPage 全面重写，移除 @apply 违规
- 新增 5 语言 i18n 键值（暂停/恢复/取消/排队中等）

src/preload/index.ts

@@ -82,7 +82,43 @@ const api = {
   scanLocalMusicWithStats: (folderPath: string) =>
     ipcRenderer.invoke('scan-local-music-with-stats', folderPath),
   parseLocalMusicMetadata: (filePaths: string[]) =>
-    ipcRenderer.invoke('parse-local-music-metadata', filePaths)
+    ipcRenderer.invoke('parse-local-music-metadata', filePaths),
+
+  // Download manager
+  downloadAdd: (task: any) => ipcRenderer.invoke('download:add', task),
+  downloadAddBatch: (tasks: any) => ipcRenderer.invoke('download:add-batch', tasks),
+  downloadPause: (taskId: string) => ipcRenderer.invoke('download:pause', taskId),
+  downloadResume: (taskId: string) => ipcRenderer.invoke('download:resume', taskId),
+  downloadCancel: (taskId: string) => ipcRenderer.invoke('download:cancel', taskId),
+  downloadCancelAll: () => ipcRenderer.invoke('download:cancel-all'),
+  downloadGetQueue: () => ipcRenderer.invoke('download:get-queue'),
+  downloadSetConcurrency: (n: number) => ipcRenderer.send('download:set-concurrency', n),
+  downloadGetCompleted: () => ipcRenderer.invoke('download:get-completed'),
+  downloadDeleteCompleted: (filePath: string) =>
+    ipcRenderer.invoke('download:delete-completed', filePath),
+  downloadClearCompleted: () => ipcRenderer.invoke('download:clear-completed'),
+  getEmbeddedLyrics: (filePath: string) =>
+    ipcRenderer.invoke('download:get-embedded-lyrics', filePath),
+  downloadProvideUrl: (taskId: string, url: string) =>
+    ipcRenderer.invoke('download:provide-url', { taskId, url }),
+  onDownloadProgress: (cb: (data: any) => void) => {
+    ipcRenderer.on('download:progress', (_event: any, data: any) => cb(data));
+  },
+  onDownloadStateChange: (cb: (data: any) => void) => {
+    ipcRenderer.on('download:state-change', (_event: any, data: any) => cb(data));
+  },
+  onDownloadBatchComplete: (cb: (data: any) => void) => {
+    ipcRenderer.on('download:batch-complete', (_event: any, data: any) => cb(data));
+  },
+  onDownloadRequestUrl: (cb: (data: any) => void) => {
+    ipcRenderer.on('download:request-url', (_event: any, data: any) => cb(data));
+  },
+  removeDownloadListeners: () => {
+    ipcRenderer.removeAllListeners('download:progress');
+    ipcRenderer.removeAllListeners('download:state-change');
+    ipcRenderer.removeAllListeners('download:batch-complete');
+    ipcRenderer.removeAllListeners('download:request-url');
+  }
 };
 
 // 创建带类型的ipcRenderer对象，暴露给渲染进程