feat: 结构化 observation 替代 statusDetail，API 层动态构造 detail

- CheckResult: statusDetail -> observation (持久化) + detail (API 动态派生)
- 存储: status_detail 列 -> observation TEXT (JSON)
- CheckerDefinition: 新增 buildDetail(observation) 方法
- 各 checker 返回结构化 observation，API 层通过 registry 调用 buildDetail
- HTTP: bodyPreview 在 status/header 失败时也提前采集
- UDP: observation 包含 durationMs，未响应归为 error failure
- CMD: 超时/输出超限时保留已收集 observation
- TCP: connectTimeMs 仅含连接建立耗时，不含 banner 等待
- 新增 buildDetail 单测和 mapCheckResult 覆盖测试
- 同步 openspec 主规范，归档 checker-observation 变更

tests/web/constants/target-table-columns.test.ts

@@ -110,10 +110,11 @@ describe("createTargetTableColumns", () => {
       colIndex: 6,
       row: makeTarget({
         latestCheck: {
+          detail: "200",
           durationMs: 12000,
           failure: null,
           matched: true,
-          statusDetail: "200",
+          observation: null,
           timestamp: "2026-01-01T00:00:00.000Z",
         },
       }),
@@ -139,10 +140,11 @@ describe("createTargetTableColumns", () => {
       colIndex: 6,
       row: makeTarget({
         latestCheck: {
+          detail: "200",
           durationMs: 123,
           failure: null,
           matched: true,
-          statusDetail: "200",
+          observation: null,
           timestamp: "2026-01-01T00:00:00.000Z",
         },
       }),

tests/web/constants/target-table-sorters.test.ts

@@ -24,10 +24,10 @@ function makeTarget(overrides: Partial<TargetStatus> = {}): TargetStatus {
 describe("statusSorter", () => {
   test("DOWN 排在 UP 前面", () => {
     const up = makeTarget({
-      latestCheck: { durationMs: 10, failure: null, matched: true, statusDetail: null, timestamp: "" },
+      latestCheck: { detail: null, durationMs: 10, failure: null, matched: true, observation: null, timestamp: "" },
     });
     const down = makeTarget({
-      latestCheck: { durationMs: 10, failure: null, matched: false, statusDetail: null, timestamp: "" },
+      latestCheck: { detail: null, durationMs: 10, failure: null, matched: false, observation: null, timestamp: "" },
     });
     expect(statusSorter(down, up)).toBeLessThan(0);
     expect(statusSorter(up, down)).toBeGreaterThan(0);
@@ -35,10 +35,10 @@ describe("statusSorter", () => {
 
   test("相同状态返回 0", () => {
     const a = makeTarget({
-      latestCheck: { durationMs: 10, failure: null, matched: true, statusDetail: null, timestamp: "" },
+      latestCheck: { detail: null, durationMs: 10, failure: null, matched: true, observation: null, timestamp: "" },
     });
     const b = makeTarget({
-      latestCheck: { durationMs: 20, failure: null, matched: true, statusDetail: null, timestamp: "" },
+      latestCheck: { detail: null, durationMs: 20, failure: null, matched: true, observation: null, timestamp: "" },
     });
     expect(statusSorter(a, b)).toBe(0);
   });
@@ -46,7 +46,7 @@ describe("statusSorter", () => {
   test("无 latestCheck 的目标排在最后", () => {
     const noCheck = makeTarget();
     const up = makeTarget({
-      latestCheck: { durationMs: 10, failure: null, matched: true, statusDetail: null, timestamp: "" },
+      latestCheck: { detail: null, durationMs: 10, failure: null, matched: true, observation: null, timestamp: "" },
     });
     expect(statusSorter(noCheck, up)).toBeGreaterThan(0);
   });
@@ -75,20 +75,20 @@ describe("availabilitySorter", () => {
 describe("latencySorter", () => {
   test("低延迟排前面", () => {
     const fast = makeTarget({
-      latestCheck: { durationMs: 50, failure: null, matched: true, statusDetail: null, timestamp: "" },
+      latestCheck: { detail: null, durationMs: 50, failure: null, matched: true, observation: null, timestamp: "" },
     });
     const slow = makeTarget({
-      latestCheck: { durationMs: 200, failure: null, matched: true, statusDetail: null, timestamp: "" },
+      latestCheck: { detail: null, durationMs: 200, failure: null, matched: true, observation: null, timestamp: "" },
     });
     expect(latencySorter(fast, slow)).toBeLessThan(0);
   });
 
   test("无延迟排最后", () => {
     const noLatency = makeTarget({
-      latestCheck: { durationMs: null, failure: null, matched: true, statusDetail: null, timestamp: "" },
+      latestCheck: { detail: null, durationMs: null, failure: null, matched: true, observation: null, timestamp: "" },
     });
     const hasLatency = makeTarget({
-      latestCheck: { durationMs: 100, failure: null, matched: true, statusDetail: null, timestamp: "" },
+      latestCheck: { detail: null, durationMs: 100, failure: null, matched: true, observation: null, timestamp: "" },
     });
     expect(latencySorter(noLatency, hasLatency)).toBeGreaterThan(0);
   });