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

src/server/middleware/error-handler.ts

@@ -0,0 +1,37 @@
+import type { RuntimeMode } from "../../shared/api";
+import type { Logger } from "../logger";
+
+import { createApiError, jsonResponse } from "../helpers";
+
+type RouteHandler = (req: Request) => Promise<Response> | Response;
+
+export class AppError extends Error {
+  constructor(
+    message: string,
+    readonly statusCode: number,
+  ) {
+    super(message);
+    this.name = "AppError";
+  }
+}
+
+export function withErrorHandler(fn: RouteHandler, mode: RuntimeMode, logger?: Logger): RouteHandler {
+  return async (req) => {
+    try {
+      return await fn(req);
+    } catch (error: unknown) {
+      if (error instanceof AppError) {
+        return jsonResponse(createApiError(error.message, error.statusCode), {
+          mode,
+          status: error.statusCode,
+        });
+      }
+
+      logger?.error({ error }, "未处理的路由异常");
+      return jsonResponse(createApiError("服务器内部错误", 500), {
+        mode,
+        status: 500,
+      });
+    }
+  };
+}