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）

scripts/generate-config-schema.ts

@@ -0,0 +1,16 @@
+import { createProbeConfigJsonSchema } from "../src/server/checker/config-contract/export";
+import { createDefaultCheckerRegistry } from "../src/server/checker/runner";
+
+const schemaPath = "probe-config.schema.json";
+const schema = `${JSON.stringify(createProbeConfigJsonSchema(createDefaultCheckerRegistry()), null, 2)}\n`;
+
+if (process.argv.includes("--check")) {
+  const existing = await Bun.file(schemaPath)
+    .text()
+    .catch(() => null);
+  if (existing !== schema) {
+    throw new Error(`${schemaPath} 未同步，请运行 bun run schema`);
+  }
+} else {
+  await Bun.write(schemaPath, schema);
+}