chore: add admin guard file that I forgot to add #199

Author: bsilkyn

frontend/src/router/guards/admin.guard.ts

@@ -0,0 +1,10 @@
+import { useAuthStore } from '@/store/authentication.store.ts';
+import { type RouteLocationRaw } from 'vue-router';
+
+export function AdminGuard(): boolean | RouteLocationRaw {
+    const { user } = useAuthStore();
+    if (user?.is_staff ?? false) {
+        return true;
+    }
+    return 'dashboard';
+}