refactor: 代码审查修复 — 错误边界、DRY抽取、测试修复、合规性改进

- P1: server.ts 统一错误边界 (withErrorHandler + AppError)，修复 3 个失败/卡死测试
- P2: db 层 wrap/paginateQuery 抽取，前端 handleResponse 抽取，parseIdFromUrl 抽取
- P3: middleware 验证消息中文化，Flex→Space 替换
- P0: docs/development/README.md 新增已知设计决策章节
- P3-11 setup 拆分已尝试回退（@testing-library/react preload 依赖无法拆分）
- P3-13 config 层测试从本次变更移除

tests/server/config.test.ts

@@ -224,7 +224,8 @@ describe("loadServerConfig", () => {
       await loadServerConfig(yamlPath);
       expect.unreachable();
     } catch (error) {
-      expect((error as Error).message).toContain("日志等级");
+      expect((error as Error).message).toContain("server.logging.level");
+      expect((error as Error).message).toContain("不在允许范围内");
     } finally {
       await rm(yamlPath, { force: true });
     }