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/execute.ts

@@ -206,12 +206,9 @@ export class TcpChecker implements CheckerDefinition<ResolvedTcpTarget> {
 
   resolve(target: RawTargetConfig, context: ResolveContext): ResolvedTcpTarget {
     const t = target as RawTargetConfig & { tcp: TcpTargetConfig; type: "tcp" };
-    const tcpDefaults = context.defaults["tcp"] as
-      | undefined
-      | { bannerReadTimeout?: number; maxBannerBytes?: number | string };
 
-    const maxBannerBytes = parseSize(t.tcp.maxBannerBytes ?? tcpDefaults?.maxBannerBytes ?? DEFAULT_MAX_BANNER_BYTES);
-    const bannerReadTimeout = t.tcp.bannerReadTimeout ?? tcpDefaults?.bannerReadTimeout ?? DEFAULT_BANNER_READ_TIMEOUT;
+    const maxBannerBytes = parseSize(t.tcp.maxBannerBytes ?? DEFAULT_MAX_BANNER_BYTES);
+    const bannerReadTimeout = t.tcp.bannerReadTimeout ?? DEFAULT_BANNER_READ_TIMEOUT;
 
     const rawExpect = target.expect as RawTcpExpectConfig | undefined;
     const resolvedExpect: ResolvedTcpExpectConfig = rawExpect