feat(远程备份): 添加连接测试功能并优化协议切换逻辑

前端添加连接测试功能，使用 getFieldsValue 获取完整表单值并打印日志
后端实现 /remote/test 接口，支持协议自动推断和连接测试
优化协议切换时的表单重置逻辑，清空相关字段并设置默认路径

backend/routes/backup.js

@@ -798,6 +798,59 @@ router.delete('/remote/targets/:id', (req, res) => {
   }
 });
 
+// 直接测试远端连接（不保存，用于添加节点前的测试）
+router.post('/remote/test', async (req, res) => {
+  try {
+    const config = req.body;
+    console.log(`[RemoteBackup] 收到连接测试请求:`, JSON.stringify(config));
+
+    if (!config.host || !config.port || !config.username) {
+      return res.status(400).json({
+        success: false,
+        message: '请提供完整的连接信息（主机、端口、用户名）',
+      });
+    }
+
+    if (!config.protocol) {
+      const port = parseInt(config.port);
+      if (port === 22 || port === 2222) {
+        config.protocol = 'sftp';
+      } else if (port === 445 || port === 139 || port === 443) {
+        config.protocol = 'smb';
+      } else if (port === 80 || port === 443 || config.url) {
+        config.protocol = 'webdav';
+      } else {
+        config.protocol = 'ftp';
+      }
+      console.log(`[RemoteBackup] 推断协议类型: ${config.protocol} (基于端口 ${config.port})`);
+    }
+
+    const result = await testRemoteConnection(config);
+    console.log(`[RemoteBackup] 连接测试结果:`, JSON.stringify(result));
+    
+    if (result.success) {
+      res.json({
+        success: true,
+        message: '连接测试成功',
+        data: result,
+      });
+    } else {
+      res.status(500).json({
+        success: false,
+        message: result.message,
+        error: result.error,
+      });
+    }
+  } catch (error) {
+    console.error('[RemoteBackup] 测试远端连接失败:', error);
+    res.status(500).json({
+      success: false,
+      message: '测试远端连接失败',
+      error: error.message,
+    });
+  }
+});
+
 // 测试远端连接
 router.post('/remote/targets/:id/test', async (req, res) => {
   try {

frontend/src/pages/RemoteBackupSettings.jsx

@@ -293,8 +293,10 @@ const RemoteBackupSettings = () => {
     try {
       setTesting(true);
       setTestStatus('testing');
-      
-      const values = await form.validateFields();
+
+      await form.validateFields();
+      const values = form.getFieldsValue(true);
+      console.log('[TestConnection] getFieldsValue(true):', JSON.stringify(values));
       const response = await api.post('/backup/remote/test', values);
       
       if (response?.success) {
@@ -832,7 +834,20 @@ const RemoteBackupSettings = () => {
           placeholder="选择协议类型"
           size="large"
           onChange={() => {
-            form.setFieldsValue({});
+            form.setFieldsValue({
+              host: undefined,
+              port: undefined,
+              username: undefined,
+              password: undefined,
+              secure: undefined,
+              privateKey: undefined,
+              passphrase: undefined,
+              share: undefined,
+              domain: undefined,
+              url: undefined,
+              authType: undefined,
+              rootPath: '/',
+            });
             setTestStatus(null);
           }}
         >