fix: make cycle regeneration atomic on type change

Make cycle regeneration synchronous in the same transaction as the member
update to ensure atomicity.

lib/membership/member.ex

@@ -191,14 +191,13 @@ defmodule Mv.Membership.Member do
 
       # Trigger cycle regeneration when membership_fee_type_id changes
       # This deletes future unpaid cycles and regenerates them with the new type/amount
-      # Note: Cycle regeneration runs asynchronously to not block the action,
+      # Note: Cycle regeneration runs synchronously in the same transaction to ensure atomicity
-      # but in test environment it runs synchronously for DB sandbox compatibility
+      # CycleGenerator uses advisory locks and transactions internally to prevent race conditions
       change after_action(fn changeset, member, _context ->
                fee_type_changed =
                  Ash.Changeset.changing_attribute?(changeset, :membership_fee_type_id)
 
                if fee_type_changed && member.membership_fee_type_id && member.join_date do
-                 regenerate_fn = fn ->
                  case regenerate_cycles_on_type_change(member) do
                    :ok ->
                      :ok
@@ -212,15 +211,6 @@ defmodule Mv.Membership.Member do
                  end
                end
 
-                 if Application.get_env(:mv, :sql_sandbox, false) do
-                   # Run synchronously in test environment for DB sandbox compatibility
-                   regenerate_fn.()
-                 else
-                   # Run asynchronously in other environments
-                   Task.start(regenerate_fn)
-                 end
-               end
-
                {:ok, member}
              end)
     end