✨ Let admins grant complimentary paid plans

Admins can give a user Maker or Shipaholic without payment from the admin user page, with an optional expiry, and revoke it again. Comped users get a "complimentary" plan status honoured by Plan.for, any live Stripe subscription is cancelled on grant, and each grant/revoke is logged as an AdminAction. The user list gains a plan column and filter, and the billing page shows the comp instead of a cancel button.