refactor: 移除顶层 defaults 配置段，简化为 target 显式字段 > 代码内置默认值

- 移除 DefaultsConfig 类型、ProbeConfig.defaults 字段
- 移除 CheckerSchemas.defaults、ResolveContext.defaults、CheckerValidationInput.defaults
- 更新所有 checker schema/resolve/validate 删除 defaults 合并逻辑
- 更新 config-loader 不再读取传递 defaults
- 更新测试、README、DEVELOPMENT、probes.example.yaml
- 重新生成 probe-config.schema.json（不含 defaults）
- 同步 delta specs 到主规范
- 归档 openspec change

src/server/checker/runner/tcp/validate.ts

@@ -9,8 +9,6 @@ import { issue, joinPath } from "../../schema/issues";
 export function validateTcpConfig(input: CheckerValidationInput): ConfigValidationIssue[] {
   const issues: ConfigValidationIssue[] = [];
 
-  issues.push(...validateTcpDefaults(input));
-
   for (let i = 0; i < input.targets.length; i++) {
     const target = input.targets[i] as unknown;
     if (!isPlainRecord(target)) continue;
@@ -30,40 +28,6 @@ function isNonNegativeFiniteNumber(value: unknown): boolean {
   return isNumber(value) && Number.isFinite(value) && value >= 0;
 }
 
-function validateTcpDefaults(input: CheckerValidationInput): ConfigValidationIssue[] {
-  const issues: ConfigValidationIssue[] = [];
-  const defaults = input.defaults["tcp"];
-  if (defaults === undefined || defaults === null || !isPlainRecord(defaults)) return issues;
-
-  const targetName = "defaults.tcp";
-
-  if (defaults["bannerReadTimeout"] !== undefined && !isNonNegativeFiniteNumber(defaults["bannerReadTimeout"])) {
-    issues.push(issue("invalid-type", "defaults.tcp.bannerReadTimeout", "必须为非负有限数字", targetName));
-  }
-
-  if (defaults["maxBannerBytes"] !== undefined) {
-    if (
-      !isString(defaults["maxBannerBytes"]) &&
-      !(
-        isNumber(defaults["maxBannerBytes"]) &&
-        Number.isFinite(defaults["maxBannerBytes"]) &&
-        defaults["maxBannerBytes"] >= 0
-      )
-    ) {
-      issues.push(issue("invalid-value", "defaults.tcp.maxBannerBytes", "必须为合法 size 值", targetName));
-    }
-  }
-
-  const allowedKeys = new Set(["bannerReadTimeout", "maxBannerBytes"]);
-  for (const key of Object.keys(defaults)) {
-    if (!allowedKeys.has(key)) {
-      issues.push(issue("unknown-field", joinPath("defaults.tcp", key), "是未知字段", targetName));
-    }
-  }
-
-  return issues;
-}
-
 function validateTcpExpect(
   target: Record<string, unknown>,
   path: string,
@@ -159,5 +123,3 @@ function validateTcpTarget(target: Record<string, unknown>, path: string): Confi
 
   return issues;
 }
-
-export { validateTcpDefaults };