feat: 重构配置校验为 TypeBox + Ajv + semantic validator，严格禁止未知字段

- 新增 config-contract 模块（TypeBox fragments、Ajv 契约校验、ConfigValidationIssue）
- CheckerDefinition 扩展为含 configKey、schemas、validate 的完整插件接口
- HTTP/Command 各自维护 contract.ts + validate.ts，校验从 resolve 中分离
- resolve 不再承担校验，只做默认值合并和路径/单位解析
- config-loader 流程: unknown → RawProbeConfig → ValidatedProbeConfig → ResolvedConfig
- 导出 probe-config.schema.json，新增 schema/schema:check 脚本
- 更新 DEVELOPMENT.md 新增 1.7 开发新 Checker 完整指引
- 同步更新 4 个 main specs（probe-config、command-checker、expect-body-checkers、checker-runner-abstraction）

src/server/checker/config-contract/issues.ts

@@ -0,0 +1,37 @@
+export interface ConfigValidationIssue {
+  code: string;
+  message: string;
+  path: string;
+  targetName?: string;
+}
+
+export function formatConfigIssues(issues: ConfigValidationIssue[]): string {
+  return issues.map(formatConfigIssue).join("\n");
+}
+
+export function issue(code: string, path: string, message: string, targetName?: string): ConfigValidationIssue {
+  return targetName === undefined ? { code, message, path } : { code, message, path, targetName };
+}
+
+export function joinPath(base: string, key: string): string {
+  if (base === "") return key;
+  if (key.startsWith("[")) return `${base}${key}`;
+  return `${base}.${key}`;
+}
+
+export function renderPath(path: string): string {
+  return path === "" ? "配置文件" : path;
+}
+
+export function throwConfigIssues(issues: ConfigValidationIssue[]): never {
+  throw new Error(formatConfigIssues(issues));
+}
+
+function formatConfigIssue(issue: ConfigValidationIssue): string {
+  if (issue.targetName) {
+    const path = issue.path.replace(/^targets\[\d+\]\.?/, "");
+    const renderedPath = path === "" ? "配置" : path;
+    return `target "${issue.targetName}" 的 ${renderedPath} ${issue.message}`;
+  }
+  return `${renderPath(issue.path)} ${issue.message}`;
+}