refactor(env, api, i18n): 更新环境配置与API代理逻辑

修改 .env.example，优化API配置说明并明确线上环境要求。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API代理逻辑，移除开发代理文件，简化代码结构，提升可维护性。

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

@@ -1,12 +1,12 @@
 import { type NextRequest } from "next/server";
 
-import { proxyLotteryApiInDev } from "@/lib/lottery-api-dev-proxy";
+import { proxyLotteryApi } from "@/lib/lottery-api-proxy";
 
 type RouteContext = { params: Promise<{ path: string[] }> };
 
 async function handle(request: NextRequest, context: RouteContext) {
   const { path } = await context.params;
-  return proxyLotteryApiInDev(request, path);
+  return proxyLotteryApi(request, path);
 }
 
 export const GET = handle;