feat: 增强 expect 规则系统，支持多种 body 校验方法和操作符

- 新增 body 分组校验：contains、regex、json（JSONPath）、css（CSS选择器）、xpath
- 新增操作符系统：equals、contains、match、empty、exists、gte、lte、gt、lt
- 新增 headers 响应头校验
- 引入 cheerio、xpath、@xmldom/xmldom 依赖
- BREAKING: expect.bodyContains 迁移至 expect.body.contains

probes.example.yaml

@@ -14,3 +14,23 @@ targets:
     expect:
       status: [200]
       maxLatencyMs: 10000
+
+  - name: "JSON API 示例"
+    url: "https://httpbin.org/json"
+    expect:
+      status: [200]
+      headers:
+        Content-Type: application/json
+      body:
+        contains: "slideshow"
+        json:
+          $.slideshow.title: "Sample Slide Show"
+
+  - name: "HTML 页面示例"
+    url: "https://httpbin.org/html"
+    expect:
+      status: [200]
+      body:
+        contains: "Moby-Dick"
+        xpath:
+          "/html/body/h1/text()": "Herman Melville - Moby-Dick"