refactor: 提取 validation.ts 和 amap.ts，统一 API 路由校验逻辑

新增 validation.ts（用户名/密码/邮箱/内容/房间名/必填字段校验）
和 amap.ts（AMAP API key 校验），消除 7 个路由中的重复验证代码。

src/app/api/room/create/route.ts

@@ -3,6 +3,7 @@ import { createRoom } from "@/lib/store";
 import { Restaurant, SceneType } from "@/types";
 import { getSceneConfig } from "@/lib/sceneConfig";
 import { apiHandler, ApiError } from "@/lib/api";
+import { requireAmapApiKey } from "@/lib/amap";
 
 interface AmapPoiV5 {
   id: string;
@@ -120,10 +121,7 @@ export const POST = apiHandler(async (req) => {
     throw new ApiError("无法获取位置信息，请允许定位权限后重试");
   }
 
-  const apiKey = process.env.AMAP_API_KEY;
-  if (!apiKey) {
-    throw new ApiError("服务配置异常，请稍后重试", 500);
-  }
+  const apiKey = requireAmapApiKey();
 
   const url = new URL("https://restapi.amap.com/v5/place/around");
   url.searchParams.set("key", apiKey);