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

src/server/checker/runner/db/normalize.ts

@@ -0,0 +1,19 @@
+import { isPlainObject } from "es-toolkit";
+
+import type { RawTargetConfig } from "../../types";
+
+import { compactExpect, normalizeContent, normalizeKeyed, normalizeValue } from "../../expect/normalize";
+
+export function normalizeTargetExpect(target: RawTargetConfig): RawTargetConfig {
+  if (target.expect === undefined || !isPlainObject(target.expect)) return target;
+  const raw = target.expect as Record<string, unknown>;
+  return {
+    ...target,
+    expect: compactExpect(raw, {
+      durationMs: normalizeValue(raw["durationMs"]),
+      result: normalizeContent(raw["result"]),
+      rowCount: normalizeValue(raw["rowCount"]),
+      rows: Array.isArray(raw["rows"]) ? raw["rows"].map((row) => normalizeKeyed(row)) : raw["rows"],
+    }),
+  };
+}