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/server/checker/store.test.ts

@@ -163,7 +163,7 @@ describe("ProbeStore", () => {
       durationMs: 150.5,
       failure: null,
       matched: true,
-      statusDetail: "200 OK",
+      observation: null,
       targetId: "test-http",
       timestamp: "2025-01-01T00:00:00.000Z",
     });
@@ -172,7 +172,7 @@ describe("ProbeStore", () => {
       durationMs: 300,
       failure: null,
       matched: true,
-      statusDetail: "200 OK",
+      observation: null,
       targetId: "test-http",
       timestamp: "2025-01-01T00:00:30.000Z",
     });
@@ -190,7 +190,7 @@ describe("ProbeStore", () => {
       durationMs: null,
       failure,
       matched: false,
-      statusDetail: null,
+      observation: null,
       targetId: "test-http",
       timestamp: "2025-01-01T00:01:00.000Z",
     });
@@ -214,7 +214,7 @@ describe("ProbeStore", () => {
         durationMs: 100 + i,
         failure: null,
         matched: true,
-        statusDetail: "200 OK",
+        observation: null,
         targetId: "test-http",
         timestamp: `2025-01-01T01:${String(i).padStart(2, "0")}:00.000Z`,
       });
@@ -302,7 +302,7 @@ describe("ProbeStore", () => {
         durationMs: 100 + index,
         failure: null,
         matched: index !== 1,
-        statusDetail: "200 OK",
+        observation: null,
         targetId: targetAId,
         timestamp,
       });
@@ -311,7 +311,7 @@ describe("ProbeStore", () => {
       durationMs: 200,
       failure: null,
       matched: true,
-      statusDetail: "200 OK",
+      observation: null,
       targetId: targetBId,
       timestamp: "2025-01-01T00:03:00.000Z",
     });
@@ -319,7 +319,7 @@ describe("ProbeStore", () => {
       durationMs: null,
       failure: { kind: "error", message: "fail", path: "request", phase: "request" },
       matched: false,
-      statusDetail: null,
+      observation: null,
       targetId: targetBId,
       timestamp: "2025-01-01T00:04:00.000Z",
     });
@@ -373,7 +373,7 @@ describe("ProbeStore", () => {
       durationMs: 100,
       failure: null,
       matched: true,
-      statusDetail: "200 OK",
+      observation: null,
       targetId: t.id,
       timestamp: "2025-01-01T00:00:00.000Z",
     });
@@ -381,7 +381,7 @@ describe("ProbeStore", () => {
       durationMs: null,
       failure: { kind: "error", message: "fail", path: "$", phase: "status" },
       matched: false,
-      statusDetail: null,
+      observation: null,
       targetId: t.id,
       timestamp: "2025-01-01T00:01:00.000Z",
     });
@@ -493,7 +493,7 @@ describe("ProbeStore", () => {
         durationMs: 100,
         failure: null,
         matched,
-        statusDetail: matched ? "200 OK" : "500 ERROR",
+        observation: null,
         targetId,
         timestamp: `2025-01-01T00:0${index}:00.000Z`,
       });
@@ -535,7 +535,7 @@ describe("ProbeStore", () => {
       durationMs: 100,
       failure: null,
       matched: false,
-      statusDetail: null,
+      observation: null,
       targetId: targetBId,
       timestamp: "2025-01-01T00:03:00.000Z",
     });
@@ -543,7 +543,7 @@ describe("ProbeStore", () => {
       durationMs: 100,
       failure: null,
       matched: true,
-      statusDetail: "200 OK",
+      observation: null,
       targetId: targetAId,
       timestamp: "2025-01-01T00:02:00.000Z",
     });
@@ -551,7 +551,7 @@ describe("ProbeStore", () => {
       durationMs: 100,
       failure: null,
       matched: false,
-      statusDetail: null,
+      observation: null,
       targetId: targetAId,
       timestamp: "2025-01-01T00:01:00.000Z",
     });
@@ -574,7 +574,7 @@ describe("ProbeStore", () => {
       durationMs: 100,
       failure: null,
       matched: true,
-      statusDetail: "200 OK",
+      observation: null,
       targetId: t.id,
       timestamp: "2020-01-01T00:00:00.000Z",
     });
@@ -582,7 +582,7 @@ describe("ProbeStore", () => {
       durationMs: 100,
       failure: null,
       matched: true,
-      statusDetail: "200 OK",
+      observation: null,
       targetId: t.id,
       timestamp: new Date().toISOString(),
     });
@@ -605,7 +605,7 @@ describe("ProbeStore", () => {
       durationMs: 100,
       failure: null,
       matched: true,
-      statusDetail: "200 OK",
+      observation: null,
       targetId: t.id,
       timestamp: new Date().toISOString(),
     });
@@ -626,7 +626,7 @@ describe("ProbeStore", () => {
       durationMs: 100,
       failure: null,
       matched: true,
-      statusDetail: "200 OK",
+      observation: null,
       targetId: t.id,
       timestamp: new Date(now - 3600000).toISOString(),
     });
@@ -634,7 +634,7 @@ describe("ProbeStore", () => {
       durationMs: 200,
       failure: null,
       matched: true,
-      statusDetail: "200 OK",
+      observation: null,
       targetId: t.id,
       timestamp: new Date(now).toISOString(),
     });