refactor(auth): migrate social login to next-auth

src/app/api/auth/[...nextauth]/route.ts

@@ -0,0 +1,19 @@
+/**
+ * NextAuth App Router 入口
+ *
+ * 路径：/api/auth/[...nextauth]
+ * 自动处理 NextAuth 所有内置路由：
+ *   /api/auth/signin/[provider]
+ *   /api/auth/callback/[provider]
+ *   /api/auth/signout
+ *   /api/auth/session
+ *   /api/auth/csrf
+ *   /api/auth/providers
+ */
+import NextAuth from "next-auth";
+
+import { authOptions } from "@/lib/auth/config";
+
+const handler = NextAuth(authOptions);
+
+export { handler as GET, handler as POST };