feat: 配置变量系统与 target id/name 双字段标识

- 新增顶层 variables 段支持 string/number/boolean 字面量
- target 字符串字段支持 、、{...} 转义语法
- 变量解析优先级: variables -> process.env -> 默认值 -> 报错
- 完整引用保留原始类型，部分引用拼接为字符串
- 变量替换在 YAML 解析后、AJV 校验前执行
- 替换仅作用于 targets，跳过 id/type 字段
- target 新增必填 id 字段作为唯一标识，name 改为可选展示名称
- 数据库存储/API/前端全面迁移到 id 标识
- 统一 checker 运行时类型检查为 es-toolkit predicates
- 同步 delta specs 到主 specs，归档 config-variables 变更

src/server/checker/expect/operator.ts

@@ -1,4 +1,5 @@
 import { isEmptyObject, isEqual, isNil, isPlainObject } from "es-toolkit";
+import { isArray } from "es-toolkit/compat";
 
 import type { ExpectOperator, ExpectValue } from "../types";
 
@@ -14,7 +15,7 @@ export function applyOperator(actual: unknown, op: ExpectOperator): boolean {
         break;
       case "empty": {
         const isEmpty =
-          isNil(actual) || actual === "" || (Array.isArray(actual) && actual.length === 0) || isEmptyObject(actual);
+          isNil(actual) || actual === "" || (isArray(actual) && actual.length === 0) || isEmptyObject(actual);
         if (expected !== isEmpty) return false;
         break;
       }
@@ -67,7 +68,7 @@ export function evaluateJsonPath(json: unknown, path: string): unknown {
     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;
+      if (!isArray(current) || idx >= current.length) return undefined;
       current = current[idx];
     } else {
       if (current === null || current === undefined) return undefined;