Aggiunge abbonamenti omaggio admin per sponsor e promozioni.

Gli admin possono concedere o revocare Premium Light/Full senza Stripe;
il piano omaggio ha priorità sui webhook e la società vede un messaggio dedicato.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/models/subscription.rb

@@ -5,6 +5,7 @@ class Subscription < ApplicationRecord
   belongs_to :club
   belongs_to :plan
   belongs_to :pending_plan, class_name: "Plan", optional: true
+  belongs_to :admin_comped_by, class_name: "AdminAccount", optional: true
 
   validates :status, inclusion: { in: STATUSES }
   validates :club_id, uniqueness: true
@@ -30,4 +31,8 @@ class Subscription < ApplicationRecord
   def plan_change_pending?
     pending_plan_id.present?
   end
+
+  def admin_comped?
+    admin_comped
+  end
 end