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

tests/server/checker/runner/db/validate.test.ts

@@ -4,13 +4,12 @@ import { validateDbConfig } from "../../../../../src/server/checker/runner/db/va
 
 describe("validateDbConfig", () => {
   test("空配置无问题", () => {
-    const result = validateDbConfig({ defaults: {}, targets: [] });
+    const result = validateDbConfig({ targets: [] });
     expect(result).toHaveLength(0);
   });
 
   test("缺少 db.url 返回错误", () => {
     const result = validateDbConfig({
-      defaults: {},
       targets: [{ id: "test", name: "test", type: "db" }],
     });
     expect(result.length).toBeGreaterThan(0);
@@ -21,7 +20,6 @@ describe("validateDbConfig", () => {
 
   test("db.url 为空字符串返回错误", () => {
     const result = validateDbConfig({
-      defaults: {},
       targets: [{ db: { url: "" }, id: "test", name: "test", type: "db" }],
     });
     const urlError = result.find((e) => e.path.includes("db.url"));
@@ -31,7 +29,6 @@ describe("validateDbConfig", () => {
 
   test("db.query 为空字符串返回错误", () => {
     const result = validateDbConfig({
-      defaults: {},
       targets: [{ db: { query: "", url: "sqlite://:memory:" }, id: "test", name: "test", type: "db" }],
     });
     const queryError = result.find((e) => e.path.includes("db.query"));
@@ -41,7 +38,6 @@ describe("validateDbConfig", () => {
 
   test("db 分组未知字段返回错误", () => {
     const result = validateDbConfig({
-      defaults: {},
       targets: [{ db: { timeout: 5, url: "sqlite://:memory:" }, id: "test", name: "test", type: "db" }],
     });
     const unknownError = result.find((e) => e.path.includes("db.timeout"));
@@ -51,7 +47,6 @@ describe("validateDbConfig", () => {
 
   test("expect.durationMs 数组简写返回错误", () => {
     const result = validateDbConfig({
-      defaults: {},
       targets: [
         {
           db: { url: "sqlite://:memory:" },
@@ -69,7 +64,6 @@ describe("validateDbConfig", () => {
 
   test("expect.rowCount 非法 operator 返回错误", () => {
     const result = validateDbConfig({
-      defaults: {},
       targets: [
         { db: { url: "sqlite://:memory:" }, expect: { rowCount: { foo: 1 } }, id: "test", name: "test", type: "db" },
       ],
@@ -81,7 +75,6 @@ describe("validateDbConfig", () => {
 
   test("expect.rows 不是数组返回错误", () => {
     const result = validateDbConfig({
-      defaults: {},
       targets: [
         { db: { url: "sqlite://:memory:" }, expect: { rows: "not-array" }, id: "test", name: "test", type: "db" },
       ],
@@ -93,7 +86,6 @@ describe("validateDbConfig", () => {
 
   test("expect.rows 元素不是对象返回错误", () => {
     const result = validateDbConfig({
-      defaults: {},
       targets: [
         { db: { url: "sqlite://:memory:" }, expect: { rows: ["not-object"] }, id: "test", name: "test", type: "db" },
       ],
@@ -105,7 +97,6 @@ describe("validateDbConfig", () => {
 
   test("expect.rows 中 regex 正则非法返回错误", () => {
     const result = validateDbConfig({
-      defaults: {},
       targets: [
         {
           db: { url: "sqlite://:memory:" },
@@ -123,7 +114,6 @@ describe("validateDbConfig", () => {
 
   test("expect 未知字段返回错误", () => {
     const result = validateDbConfig({
-      defaults: {},
       targets: [{ db: { url: "sqlite://:memory:" }, expect: { status: [200] }, id: "test", name: "test", type: "db" }],
     });
     const unknownError = result.find((e) => e.path.includes("expect.status"));
@@ -133,7 +123,6 @@ describe("validateDbConfig", () => {
 
   test("有效配置无错误", () => {
     const result = validateDbConfig({
-      defaults: {},
       targets: [
         {
           db: { query: "SELECT 1", url: "sqlite://:memory:" },
@@ -149,7 +138,6 @@ describe("validateDbConfig", () => {
 
   test("忽略非 db 类型 target", () => {
     const result = validateDbConfig({
-      defaults: {},
       targets: [{ id: "test", name: "test", type: "http" }],
     });
     expect(result).toHaveLength(0);
@@ -157,7 +145,6 @@ describe("validateDbConfig", () => {
 
   test("多个 db target 分别校验", () => {
     const result = validateDbConfig({
-      defaults: {},
       targets: [
         { db: { url: "sqlite://:memory:" }, id: "db1", name: "db1", type: "db" },
         { db: { url: "" }, id: "db2", name: "db2", type: "db" },