refactor: checker 模块内聚化 — 每个 checker 自包含于独立目录

将 checker 架构重构为完全内聚模式：每个 checker 目录包含自身的
types、schema、validate、execute、expect 和 index，新增 checker
只需创建一个目录并在 runner/index.ts 添加一行注册。

主要变更：
- runner/shared/ 拆分：断言基础设施迁入 checker/expect/，
  body.ts 迁入 http/，text.ts 迁入 command/
- config-contract/ 重命名为 schema/，schema.ts → builder.ts
- size.ts + parseDuration 合并为 utils.ts
- 顶层 types.ts 改为 base interface + index signature，
  checker 专属类型下沉到各自 types.ts
- runner/index.ts 改为显式数组注册模式
- 更新 DEVELOPMENT.md 项目结构和开发新 Checker 指南

src/server/checker/expect/operator.ts

@@ -0,0 +1,79 @@
+import { isEmptyObject, isEqual, isNil, isPlainObject } from "es-toolkit";
+
+import type { ExpectOperator, ExpectValue } from "../types";
+
+const OPERATOR_KEYS = new Set(["contains", "empty", "equals", "exists", "gt", "gte", "lt", "lte", "match"]);
+
+export function applyOperator(actual: unknown, op: ExpectOperator): boolean {
+  for (const [key, expected] of Object.entries(op)) {
+    if (expected === undefined) continue;
+
+    switch (key) {
+      case "contains":
+        if (!String(actual).includes(expected as string)) return false;
+        break;
+      case "empty": {
+        const isEmpty =
+          isNil(actual) || actual === "" || (Array.isArray(actual) && actual.length === 0) || isEmptyObject(actual);
+        if (expected !== isEmpty) return false;
+        break;
+      }
+      case "equals":
+        if (!isEqual(actual, expected)) return false;
+        break;
+      case "exists":
+        if (expected) {
+          if (actual === undefined) return false;
+        } else {
+          if (actual !== undefined) return false;
+        }
+        break;
+      case "gt":
+        if (!(Number(actual) > (expected as number))) return false;
+        break;
+      case "gte":
+        if (!(Number(actual) >= (expected as number))) return false;
+        break;
+      case "lt":
+        if (!(Number(actual) < (expected as number))) return false;
+        break;
+      case "lte":
+        if (!(Number(actual) <= (expected as number))) return false;
+        break;
+      case "match":
+        if (!new RegExp(expected as string).test(String(actual))) return false;
+        break;
+    }
+  }
+
+  return true;
+}
+
+export function checkExpectValue(actual: unknown, expected: ExpectValue): boolean {
+  if (isPlainObject(expected) && Object.keys(expected).some((key) => OPERATOR_KEYS.has(key))) {
+    return applyOperator(actual, expected as ExpectOperator);
+  }
+  return applyOperator(actual, { equals: expected as Exclude<ExpectValue, ExpectOperator> });
+}
+
+export function evaluateJsonPath(json: unknown, path: string): unknown {
+  if (!path.startsWith("$.")) return undefined;
+
+  const segments = path.slice(2).split(".");
+  let current: unknown = json;
+
+  for (const seg of segments) {
+    const bracketMatch = /^(.+?)\[(\d+)\]$/.exec(seg);
+    if (bracketMatch) {
+      current = (current as Record<string, unknown>)?.[bracketMatch[1]!];
+      const idx = parseInt(bracketMatch[2]!, 10);
+      if (!Array.isArray(current) || idx >= current.length) return undefined;
+      current = current[idx];
+    } else {
+      if (current === null || current === undefined) return undefined;
+      current = (current as Record<string, unknown>)[seg];
+    }
+  }
+
+  return current;
+}