🔧 优化大文件上传支持

前端改进:
- 添加axios上传请求30分钟超时配置

Nginx改进:
- 增加代理超时时间到30分钟（1800秒）
- 添加 proxy_request_buffering off 避免大文件缓存到磁盘
- 添加 proxy_buffering off 禁用响应缓冲
- 优化 client_body_buffer_size

修复 ERR_HTTP2_PING_FAILED / Network Error 问题

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/app.js

@@ -1436,6 +1436,7 @@ handleDragLeave(e) {
             'Authorization': `Bearer ${this.token}`,
             'Content-Type': 'multipart/form-data'
           },
+          timeout: 30 * 60 * 1000, // 30分钟超时，支持大文件上传
           onUploadProgress: (progressEvent) => {
             this.uploadProgress = Math.round((progressEvent.loaded * 100) / progressEvent.total);
             this.uploadedBytes = progressEvent.loaded;