Fix: Plugin loader import + games model name + loading state

- Import plugin loader in admin-nav.ts so plugins actually register
- Fix Prisma model name from 'gameRoom' to 'gameRooms'
- Add loading skeleton for games admin page

src/lib/admin-nav.ts

@@ -18,6 +18,7 @@ import {
 	Wrench,
 } from "lucide-react";
 import { pluginRegistry } from "@/lib/plugins";
+import "@/lib/plugins/loader";
 
 export interface AdminHubTab {
 	href: string;