fix(membership-fees): add DB constraints for enum and decimal precision

lib/membership_fees/membership_fee_cycle.ex

@@ -65,7 +65,10 @@ defmodule Mv.MembershipFees.MembershipFeeCycle do
     attribute :amount, :decimal do
       allow_nil? false
       public? true
-      description "Fee amount for this cycle (stored for audit trail)"
+
+      description "Fee amount for this cycle (stored for audit trail, non-negative, max 2 decimal places)"
+
+      constraints min: 0, scale: 2
     end
 
     attribute :status, :atom do