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/dns/normalize.test.ts

@@ -0,0 +1,87 @@
+import { describe, expect, test } from "bun:test";
+
+import { normalizeAuthoringConfig } from "../../../../../src/server/checker/normalizer";
+import { checkerRegistry } from "../../../../../src/server/checker/runner";
+import { validateProbeConfigContract } from "../../../../../src/server/checker/schema/validate";
+
+describe("DNS normalize", () => {
+  test("ValueMatcher 简写被展开", () => {
+    const result = normalizeAuthoringConfig(
+      {
+        targets: [
+          {
+            dns: { name: "example.com", resolver: "server", server: "8.8.8.8" },
+            expect: { durationMs: 1000, valueCount: { gte: 1 } },
+            id: "dns-test",
+            type: "dns",
+          },
+        ],
+      },
+      checkerRegistry,
+    );
+    expect(result.issues).toHaveLength(0);
+    const target = (result.config as { targets: Array<{ expect: Record<string, unknown> }> }).targets[0]!;
+    expect(target.expect["durationMs"]).toEqual({ equals: 1000 });
+    expect(target.expect["valueCount"]).toEqual({ gte: 1 });
+  });
+
+  test("ContentExpectations 简写被展开", () => {
+    const result = normalizeAuthoringConfig(
+      {
+        targets: [
+          {
+            dns: { name: "example.com", resolver: "server", server: "8.8.8.8" },
+            expect: { result: [{ contains: "NOERROR" }] },
+            id: "dns-test",
+            type: "dns",
+          },
+        ],
+      },
+      checkerRegistry,
+    );
+    expect(result.issues).toHaveLength(0);
+    const target = (result.config as { targets: Array<{ expect: Record<string, unknown> }> }).targets[0]!;
+    const resultExpect = target.expect["result"] as Array<Record<string, unknown>>;
+    expect(resultExpect[0]!["kind"]).toBe("value");
+    expect((resultExpect[0]!["matcher"] as Record<string, unknown>)["contains"]).toBe("NOERROR");
+  });
+
+  test("DNS authoring 简写经 normalize 后通过 normalized contract 校验", () => {
+    const result = normalizeAuthoringConfig(
+      {
+        targets: [
+          {
+            dns: { name: "example.com", resolver: "server", server: "8.8.8.8" },
+            expect: { durationMs: 1000, result: [{ contains: "NOERROR" }], valueCount: { gte: 1 } },
+            id: "dns-test",
+            type: "dns",
+          },
+        ],
+      },
+      checkerRegistry,
+    );
+    expect(result.issues).toHaveLength(0);
+    const contract = validateProbeConfigContract(result.config, checkerRegistry);
+    expect(contract.config).not.toBeNull();
+    expect(contract.issues).toHaveLength(0);
+  });
+
+  test("DNS system 模式 ValueMatcher 简写被展开", () => {
+    const result = normalizeAuthoringConfig(
+      {
+        targets: [
+          {
+            dns: { name: "example.com", resolver: "system" },
+            expect: { durationMs: 500, valueCount: { gte: 1 } },
+            id: "dns-system-test",
+            type: "dns",
+          },
+        ],
+      },
+      checkerRegistry,
+    );
+    expect(result.issues).toHaveLength(0);
+    const target = (result.config as { targets: Array<{ expect: Record<string, unknown> }> }).targets[0]!;
+    expect(target.expect["durationMs"]).toEqual({ equals: 500 });
+  });
+});