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）

src/server/checker/runner/registry.ts

@@ -1,13 +1,17 @@
-import type { Checker } from "./types";
+import type { CheckerDefinition } from "./types";
 
 export class CheckerRegistry {
+  get definitions(): CheckerDefinition[] {
+    return [...this.checkers.values()];
+  }
+
   get supportedTypes(): string[] {
     return [...this.checkers.keys()];
   }
 
-  private checkers = new Map<string, Checker>();
+  private checkers = new Map<string, CheckerDefinition>();
 
-  get(type: string): Checker {
+  get(type: string): CheckerDefinition {
     const checker = this.checkers.get(type);
     if (!checker) {
       throw new Error(`不支持的 probe type: "${type}"`);
@@ -15,12 +19,16 @@ export class CheckerRegistry {
     return checker;
   }
 
-  register(checker: Checker): void {
+  register(checker: CheckerDefinition): void {
     if (this.checkers.has(checker.type)) {
       throw new Error(`Checker type "${checker.type}" 已注册`);
     }
     this.checkers.set(checker.type, checker);
   }
+
+  tryGet(type: string): CheckerDefinition | undefined {
+    return this.checkers.get(type);
+  }
 }
 
 export const checkerRegistry = new CheckerRegistry();