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

tests/web/components/OverviewTab.test.tsx

@@ -10,7 +10,7 @@ describe("OverviewTab", () => {
   const target: TargetStatus = {
     currentStreak: null,
     group: "default",
-    id: 1,
+    id: "1",
     interval: "30s",
     latestCheck: {
       durationMs: 100,
@@ -40,7 +40,7 @@ describe("OverviewTab", () => {
       totalChecks: 20,
       upChecks: 19,
     },
-    targetId: 1,
+    targetId: "1",
     trend: [],
     window: { bucket: "1h", from: "", to: "" },
   };

tests/web/components/TargetBoard.test.tsx

@@ -20,7 +20,7 @@ describe("TargetBoard", () => {
     {
       currentStreak: null,
       group: "default",
-      id: 1,
+      id: "1",
       interval: "30s",
       latestCheck: null,
       name: "target-1",
@@ -32,7 +32,7 @@ describe("TargetBoard", () => {
     {
       currentStreak: null,
       group: "production",
-      id: 2,
+      id: "2",
       interval: "30s",
       latestCheck: null,
       name: "target-2",

tests/web/components/TargetDetailDrawer.test.tsx

@@ -10,7 +10,7 @@ describe("TargetDetailDrawer", () => {
   const target: TargetStatus = {
     currentStreak: null,
     group: "default",
-    id: 1,
+    id: "1",
     interval: "30s",
     latestCheck: {
       durationMs: 100,
@@ -40,7 +40,7 @@ describe("TargetDetailDrawer", () => {
       totalChecks: 20,
       upChecks: 19,
     },
-    targetId: 1,
+    targetId: "1",
     trend: [],
     window: { bucket: "1h", from: "", to: "" },
   };

tests/web/components/TargetGroup.test.tsx

@@ -16,7 +16,7 @@ describe("TargetGroup", () => {
     {
       currentStreak: null,
       group: "default",
-      id: 1,
+      id: "1",
       interval: "30s",
       latestCheck: {
         durationMs: 100,
@@ -34,7 +34,7 @@ describe("TargetGroup", () => {
     {
       currentStreak: null,
       group: "default",
-      id: 2,
+      id: "2",
       interval: "30s",
       latestCheck: {
         durationMs: 100,