feat(remote): 实现文件上传真实进度显示

- 使用分块上传替代一次性上传
- 调用 /upload/start → /upload/chunk → /upload/merge 接口
- 通过 IPC 事件实时推送上传进度到前端
- 修复 merge 时未使用目标路径的问题

remote/src/services/file/FileService.js

@@ -91,9 +91,13 @@ class FileService {
     }
   }
 
-  mergeChunks(fileId, totalChunks, filename) {
+  mergeChunks(fileId, totalChunks, filename, targetPath) {
     try {
-      const filePath = path.normalize(filename);
+      let targetDir = targetPath || 'C:\\';
+      if (!fs.existsSync(targetDir)) {
+        fs.mkdirSync(targetDir, { recursive: true });
+      }
+      const filePath = path.join(targetDir, filename);
       const dir = path.dirname(filePath);
       
       if (!fs.existsSync(dir)) {