feat: implement subscription (#92)

auth.d.ts

@@ -0,0 +1,15 @@
+import { Subscription } from "@/types";
+import "next-auth";
+
+declare module "next-auth" {
+  interface User {
+    id: string;
+    usage: number;
+    stripeId: number;
+    subscription: Subscription;
+  }
+
+  interface Session {
+    user: User;
+  }
+}