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/expect/normalize.ts

@@ -0,0 +1,50 @@
+import { isPlainObject } from "es-toolkit";
+
+import { resolveContentExpectations } from "./content";
+import { CONTENT_EXTRACTOR_KEY_SET, MATCHER_KEY_SET } from "./keys";
+import { isValueMatcherObject, isValueMatcherPrimitive, resolveValueExpectation } from "./value";
+
+type ExpectRecord = Record<string, unknown>;
+
+export function compactExpect(original: ExpectRecord, overrides: ExpectRecord): ExpectRecord {
+  const result: ExpectRecord = {};
+  for (const [key, value] of Object.entries(original)) {
+    if (value !== undefined) result[key] = value;
+  }
+  for (const [key, value] of Object.entries(overrides)) {
+    if (value !== undefined) result[key] = value;
+  }
+  return result;
+}
+
+export function normalizeContent(value: unknown): unknown {
+  if (value === undefined) return undefined;
+  if (!Array.isArray(value)) return value;
+  return (value as unknown[]).map((entry): unknown => {
+    if (!canNormalizeContentEntry(entry)) return entry;
+    const resolved = resolveContentExpectations([entry] as never);
+    return resolved?.[0];
+  });
+}
+
+export function normalizeKeyed(value: unknown): unknown {
+  if (value === undefined) return undefined;
+  if (!isPlainObject(value)) return value;
+  return Object.entries(value as ExpectRecord).map(([key, item]) => ({ key, matcher: normalizeValue(item) }));
+}
+
+export function normalizeValue(value: unknown): unknown {
+  if (value === undefined) return undefined;
+  if (isValueMatcherPrimitive(value) || isValueMatcherObject(value)) return resolveValueExpectation(value);
+  return value;
+}
+
+function canNormalizeContentEntry(value: unknown): boolean {
+  if (!isPlainObject(value)) return false;
+  const keys = Object.keys(value);
+  const extractorKeys = keys.filter((key) => CONTENT_EXTRACTOR_KEY_SET.has(key));
+  const matcherKeys = keys.filter((key) => MATCHER_KEY_SET.has(key));
+  if (extractorKeys.length === 0) return matcherKeys.length > 0 && matcherKeys.length === keys.length;
+  if (extractorKeys.length !== 1 || matcherKeys.length > 0 || keys.length !== 1) return false;
+  return isPlainObject((value as ExpectRecord)[extractorKeys[0]!]);
+}