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/auth/login_003.json

@@ -0,0 +1,26 @@
+{
+  "name": "user_login_003",
+  "request": {
+    "path": "/v1/auth/login",
+    "method": "POST",
+    "headers": {
+      "Content-Type": "application/json",
+      "Authorization": "eyJhbGciOiJIUzI1NiIsInR5cCI6",
+      "host": "127.0.0.1:8080"
+    },
+    "body": {
+      "username": "user003",
+      "password": "password123"
+    }
+  },
+  "response": {
+    "status": 200,
+    "headers": {
+      "Content-Type": "application/json"
+    },
+    "body": "{\"code\":0,\"message\":\"登录成功\",\"data\":{\"token\":\"eyJhbGciOiJIUzI1NiIsInR5cCI6\",\"userId\":10003,\"username\":\"user003\",\"role\":\"administrator\"}}"
+  },
+  "settings": {
+    "delay_ms": 2000
+  }
+}