feat: mock配置迁移至JSON格式并修复body匹配

- 将mock配置从YAML格式迁移到JSON格式
- 修复JSON字符串格式body匹配失败问题
- 添加MCP功能模块
- 更新mock-spec.md规范文档

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

mocks/v1/data/export.json

@@ -0,0 +1,18 @@
+{
+  "name": "data_export",
+  "request": {
+    "method": "POST",
+    "path": "/v1/data/export",
+    "headers": {
+      "Content-Type": "application/xml"
+    },
+    "body": "<?xml version=\"1.0\" encoding=\"UTF-8\"?><request><userId>10001</userId><format>xml</format></request>"
+  },
+  "response": {
+    "status": 200,
+    "headers": {
+      "Content-Type": "application/xml"
+    },
+    "body": "<?xml version=\"1.0\" encoding=\"UTF-8\"?><response><code>0</code><message>导出成功</message><data><user><id>10001</id><name>管理员</name><email>admin@example.com</email></user></data></response>"
+  }
+}