fix(admin): await user.save() without callback in createAdmin

Mongoose 7 removed callback support on Model.prototype.save(),
so the seeder threw 'no longer accepts a callback' on every
boot (caught and logged, non-fatal, but noisy and the success
path never ran). Await the promise and log on success.

scripts/adminUser.js

@@ -33,12 +33,8 @@ const createAdmin = async () => {
       gamesToAccess: [],
     })
 
-    await user.save((err) => {
-      console.log('Admin user successfully created')
-      if (err) {
-        return console.error('Could not save admin user')
-      }
-    })
+    await user.save()
+    console.log('Admin user successfully created')
   } catch (err) {
     return console.error(
       'Server Error: Could not create admin user' + err.message