feat: 新增 TCP checker，支持端口可达性探测与 banner 读取

- 新增 src/server/checker/runner/tcp/ 自包含目录（types/schema/validate/execute/expect）
- 注册 TcpChecker 到 checkerRegistry，schema/engine/store/config-loader 自动委托
- 支持 expect.connected 正反向语义（默认期待可达，可配置期待不可达）
- 支持 readBanner opt-in banner 读取，受 bannerReadTimeout + maxBannerBytes 双重限制
- 复用电有 expect/operator/duration/failure 基础设施
- 新增 3 个测试文件 51 条用例（execute/validate/expect），全量 634 测试通过
- 更新 README/DEVELOPMENT/probes.example.yaml，新增 tcp-checker capability spec

tests/server/checker/runner/registry.test.ts

@@ -66,8 +66,8 @@ describe("CheckerRegistry", () => {
     const second = createDefaultCheckerRegistry();
     first.register(createChecker("custom"));
 
-    expect(first.supportedTypes).toEqual(["http", "cmd", "db", "custom"]);
-    expect(second.supportedTypes).toEqual(["http", "cmd", "db"]);
+    expect(first.supportedTypes).toEqual(["http", "cmd", "db", "tcp", "custom"]);
+    expect(second.supportedTypes).toEqual(["http", "cmd", "db", "tcp"]);
     expect(
       first.definitions.every(
         (checker) => checker.schemas.config && checker.schemas.defaults && checker.schemas.expect,