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

src/server/routes/targets.ts

@@ -0,0 +1,36 @@
+import type { RuntimeMode, TargetStatus } from "../../shared/api";
+import type { ProbeStore } from "../checker/store";
+import { formatDuration, jsonResponse, mapCheckResult } from "../helpers";
+
+export function handleTargets(store: ProbeStore, method: string, mode: RuntimeMode): Response {
+  const targets = store.getTargets();
+  const latestChecksMap = store.getLatestChecksMap();
+  const allStats = store.getAllTargetStats();
+
+  const result: TargetStatus[] = targets.map((target) => {
+    const latest = latestChecksMap.get(target.id) ?? null;
+    const stats = allStats.get(target.id) ?? { totalChecks: 0, availability: 0 };
+    const recentSamples = store.getRecentSamples(target.id, 30);
+
+    return {
+      id: target.id,
+      name: target.name,
+      type: target.type,
+      target: target.target,
+      group: target.grp,
+      interval: formatDuration(target.interval_ms),
+      latestCheck: latest ? mapCheckResult(latest) : null,
+      recentSamples: recentSamples.map((s) => ({
+        timestamp: s.timestamp,
+        durationMs: s.duration_ms,
+        up: s.matched === 1,
+      })),
+      stats: {
+        totalChecks: stats.totalChecks,
+        availability: stats.availability,
+      },
+    };
+  });
+
+  return jsonResponse(result, { method, mode });
+}