refactor(env, i18n, http): 更新环境配置与错误提示信息

修改 .env.example，简化 API 配置说明并明确生产环境要求。更新多语言错误提示，确保用户在未启用 API 代理时获得清晰反馈。重构 admin-http.ts，优化 API 基础 URL 的解析逻辑，提升代码可维护性。

src/app/api/[...path]/route.ts

@@ -0,0 +1,16 @@
+import { type NextRequest } from "next/server";
+
+import { proxyLotteryApiInDev } from "@/lib/lottery-api-dev-proxy";
+
+type RouteContext = { params: Promise<{ path: string[] }> };
+
+async function handle(request: NextRequest, context: RouteContext) {
+  const { path } = await context.params;
+  return proxyLotteryApiInDev(request, path);
+}
+
+export const GET = handle;
+export const POST = handle;
+export const PUT = handle;
+export const PATCH = handle;
+export const DELETE = handle;