feat(remote): 实现文件下载真实进度显示

- 下载改用流式读取，计算真实进度百分比
- 通过 IPC 事件实时推送进度到前端
- 支持 Content-Length 计算下载进度

electron/preload.ts

@@ -19,6 +19,11 @@ contextBridge.exposeInMainWorld('electronAPI', {
     ipcRenderer.on('remote-clipboard-auto-sync', handler);
     return () => ipcRenderer.removeListener('remote-clipboard-auto-sync', handler);
   },
+  onDownloadProgress: (callback: (data: { progress: number; id: string }) => void) => {
+    const handler = (_event: Electron.IpcRendererEvent, data: { progress: number; id: string }) => callback(data);
+    ipcRenderer.on('download-progress', handler);
+    return () => ipcRenderer.removeListener('download-progress', handler);
+  },
   clipboardReadText: () => ipcRenderer.invoke('clipboard-read-text'),
   clipboardWriteText: (text: string) => ipcRenderer.invoke('clipboard-write-text', text),
   remoteFetchDrives: (serverHost: string, port: number, password?: string) => 
@@ -27,6 +32,6 @@ contextBridge.exposeInMainWorld('electronAPI', {
     ipcRenderer.invoke('remote-fetch-files', serverHost, port, filePath, password),
   remoteUploadFile: (serverHost: string, port: number, filePath: string, remotePath: string, password?: string) => 
     ipcRenderer.invoke('remote-upload-file', serverHost, port, filePath, remotePath, password),
-  remoteDownloadFile: (serverHost: string, port: number, fileName: string, remotePath: string, localPath: string, password?: string) => 
-    ipcRenderer.invoke('remote-download-file', serverHost, port, fileName, remotePath, localPath, password),
+  remoteDownloadFile: (id: string, serverHost: string, port: number, fileName: string, remotePath: string, localPath: string, password?: string) => 
+    ipcRenderer.invoke('remote-download-file', id, serverHost, port, fileName, remotePath, localPath, password),
 })