refactor: 将 checker normalize 职责下沉到各 runner 目录

- 新增 CheckerDefinition.normalize 必需方法，typecheck 兜底遗漏实现
- 新增 expect/normalize.ts 共享 helper（compactExpect、normalizeValue、
  normalizeContent、normalizeKeyed）
- 为 HTTP、Cmd、DB、TCP、UDP、ICMP、LLM、WS、DNS 各新增独立 normalize.ts
- 简化 normalizer.ts：删除所有 checker type switch，改为 registry 委托
- 修复 DNS authoring 简写 bug：durationMs、valueCount、result 等字段
  现可通过完整加载链路
- 新增 DNS 回归测试和 registry 级合同测试
- 更新 docs/development/checker.md：补充 normalize 规范、文件结构、
  测试要求和 checklist

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

@@ -2,7 +2,7 @@ import { Type } from "@sinclair/typebox";
 import { describe, expect, test } from "bun:test";
 
 import type { Checker } from "../../../../src/server/checker/runner/types";
-import type { CheckResult, ResolvedTargetBase } from "../../../../src/server/checker/types";
+import type { CheckResult, RawTargetConfig, ResolvedTargetBase } from "../../../../src/server/checker/types";
 
 import { createDefaultCheckerRegistry } from "../../../../src/server/checker/runner";
 import { CheckerRegistry } from "../../../../src/server/checker/runner/registry";
@@ -12,6 +12,7 @@ function createChecker(type: string): Checker {
     buildDetail: () => null,
     configKey: type,
     execute: () => Promise.resolve<CheckResult>({} as unknown as CheckResult),
+    normalize: (t: RawTargetConfig) => t,
     resolve: () => ({}) as unknown as ResolvedTargetBase,
     schemas: {
       authoring: {