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

test/membership_fees/membership_fee_cycle_test.exs

@@ -166,6 +166,30 @@ defmodule Mv.MembershipFees.MembershipFeeCycleTest do
       assert {:error, error} = Ash.create(MembershipFeeCycle, attrs)
       assert error_on_field?(error, :status)
     end
+
+    test "rejects negative amount", %{member: member, fee_type: fee_type} do
+      attrs = %{
+        cycle_start: ~D[2025-04-01],
+        amount: Decimal.new("-50.00"),
+        member_id: member.id,
+        membership_fee_type_id: fee_type.id
+      }
+
+      assert {:error, error} = Ash.create(MembershipFeeCycle, attrs)
+      assert error_on_field?(error, :amount)
+    end
+
+    test "accepts zero amount", %{member: member, fee_type: fee_type} do
+      attrs = %{
+        cycle_start: ~D[2025-05-01],
+        amount: Decimal.new("0.00"),
+        member_id: member.id,
+        membership_fee_type_id: fee_type.id
+      }
+
+      assert {:ok, cycle} = Ash.create(MembershipFeeCycle, attrs)
+      assert Decimal.equal?(cycle.amount, Decimal.new("0.00"))
+    end
   end
 
   describe "uniqueness constraint" do