refactor: 全面优化后端代码质量与架构

- app.ts 单体路由拆分为 routes/ + helpers + middleware + static 独立模块
- 类型去重：CheckFailure/CheckResult 以 shared/api.ts 为唯一源头，收紧 phase 联合类型
- es-toolkit 替换：isPlainObject/isNil/isEmptyObject/isEqual/isError/Semaphore/groupBy
- Bun 内置 API：Object.fromEntries 替代手写 headersToRecord
- bun:sqlite 规范：prepare() → query() 利用内置缓存，避免 N+1 查询
- 新增 getLatestChecksMap/allGetTargetStats 批量查询方法
- 新增 backend-code-quality/api-route-separation/batch-data-queries 规范
- 补充 openspec/config.yaml 后端开发规范与 DEVELOPMENT.md 后端开发指引

tests/server/checker/store.test.ts

@@ -297,4 +297,75 @@ describe("ProbeStore", () => {
 
     cascadeStore.close();
   });
+
+  test("getLatestChecksMap 返回所有 target 的最新 check", () => {
+    const targets = store.getTargets();
+    const map = store.getLatestChecksMap();
+    expect(map).toBeInstanceOf(Map);
+
+    for (const target of targets) {
+      const latest = map.get(target.id);
+      if (latest) {
+        expect(latest.target_id).toBe(target.id);
+      }
+    }
+  });
+
+  test("getLatestChecksMap 对无记录的 target 不包含 key", () => {
+    const freshStore = new ProbeStore(join(tempDir, "fresh-map.db"));
+    freshStore.syncTargets([
+      {
+        type: "http",
+        name: "no-records",
+        group: "default",
+        http: { url: "http://no.records", method: "GET", headers: {}, maxBodyBytes: 104857600 },
+        intervalMs: 30000,
+        timeoutMs: 10000,
+      },
+    ]);
+
+    const map = freshStore.getLatestChecksMap();
+    expect(map.size).toBe(0);
+
+    freshStore.close();
+  });
+
+  test("getAllTargetStats 返回所有 target 的聚合统计", () => {
+    const targets = store.getTargets();
+    const t1Id = targets[0]!.id;
+    const t2Id = targets[1]!.id;
+
+    const stats = store.getAllTargetStats();
+    expect(stats).toBeInstanceOf(Map);
+
+    const stats1 = stats.get(t1Id);
+    expect(stats1).toBeDefined();
+    expect(stats1!.totalChecks).toBeGreaterThan(0);
+    expect(stats1!.availability).toBeGreaterThanOrEqual(0);
+
+    const stats2 = stats.get(t2Id);
+    if (stats2) {
+      expect(stats2!.totalChecks).toBe(0);
+      expect(stats2!.availability).toBe(0);
+    }
+  });
+
+  test("getAllTargetStats 对无记录的 target 不包含 key", () => {
+    const freshStore = new ProbeStore(join(tempDir, "fresh-stats.db"));
+    freshStore.syncTargets([
+      {
+        type: "http",
+        name: "no-stats",
+        group: "default",
+        http: { url: "http://no.stats", method: "GET", headers: {}, maxBodyBytes: 104857600 },
+        intervalMs: 30000,
+        timeoutMs: 10000,
+      },
+    ]);
+
+    const stats = freshStore.getAllTargetStats();
+    expect(stats.size).toBe(0);
+
+    freshStore.close();
+  });
 });