feat: 重构配置校验为 TypeBox + Ajv + semantic validator，严格禁止未知字段

- 新增 config-contract 模块（TypeBox fragments、Ajv 契约校验、ConfigValidationIssue）
- CheckerDefinition 扩展为含 configKey、schemas、validate 的完整插件接口
- HTTP/Command 各自维护 contract.ts + validate.ts，校验从 resolve 中分离
- resolve 不再承担校验，只做默认值合并和路径/单位解析
- config-loader 流程: unknown → RawProbeConfig → ValidatedProbeConfig → ResolvedConfig
- 导出 probe-config.schema.json，新增 schema/schema:check 脚本
- 更新 DEVELOPMENT.md 新增 1.7 开发新 Checker 完整指引
- 同步更新 4 个 main specs（probe-config、command-checker、expect-body-checkers、checker-runner-abstraction）

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

@@ -1,16 +1,25 @@
+import { Type } from "@sinclair/typebox";
 import { describe, expect, test } from "bun:test";
 
 import type { Checker } from "../../../../src/server/checker/runner/types";
 import type { CheckResult, ResolvedTarget } from "../../../../src/server/checker/types";
 
+import { createDefaultCheckerRegistry } from "../../../../src/server/checker/runner";
 import { CheckerRegistry } from "../../../../src/server/checker/runner/registry";
 
 function createChecker(type: string): Checker {
   return {
+    configKey: type,
     execute: () => Promise.resolve<CheckResult>({} as unknown as CheckResult),
     resolve: () => ({}) as unknown as ResolvedTarget,
+    schemas: {
+      config: Type.Object({}, { additionalProperties: false }),
+      defaults: Type.Object({}, { additionalProperties: false }),
+      expect: Type.Object({}, { additionalProperties: false }),
+    },
     serialize: () => ({ config: "", target: "" }),
     type,
+    validate: () => [],
   };
 }
 
@@ -39,4 +48,30 @@ describe("CheckerRegistry", () => {
     registry.register(createChecker("command"));
     expect(registry.supportedTypes).toEqual(["http", "command"]);
   });
+
+  test("definitions 返回注册定义", () => {
+    const registry = new CheckerRegistry();
+    const checker = createChecker("http");
+    registry.register(checker);
+    expect(registry.definitions).toEqual([checker]);
+  });
+
+  test("tryGet 未注册返回 undefined", () => {
+    const registry = new CheckerRegistry();
+    expect(registry.tryGet("missing")).toBeUndefined();
+  });
+
+  test("默认 registry 创建 fresh 实例且互不污染", () => {
+    const first = createDefaultCheckerRegistry();
+    const second = createDefaultCheckerRegistry();
+    first.register(createChecker("custom"));
+
+    expect(first.supportedTypes).toEqual(["http", "command", "custom"]);
+    expect(second.supportedTypes).toEqual(["http", "command"]);
+    expect(
+      first.definitions.every(
+        (checker) => checker.schemas.config && checker.schemas.defaults && checker.schemas.expect,
+      ),
+    ).toBe(true);
+  });
 });