refactor: improve SetMembershipFeeStartDate change module

- Add warning logging for unexpected errors (not missing prerequisites)
- Use CalendarCycles.interval() type instead of generic atom()
- Update moduledoc to reflect actual usage (no where clause needed)

lib/membership_fees/changes/set_membership_fee_start_date.ex

@@ -18,14 +18,16 @@ defmodule Mv.MembershipFees.Changes.SetMembershipFeeStartDate do
 
       create :create_member do
         # ...
-        change Mv.MembershipFees.Changes.SetMembershipFeeStartDate do
-          where [present(:membership_fee_type_id), present(:join_date)]
-        end
+        change Mv.MembershipFees.Changes.SetMembershipFeeStartDate
       end
 
+  The change module handles all prerequisite checks internally (join_date, membership_fee_type_id).
+  If any required data is missing, the changeset is returned unchanged with a warning logged.
   """
   use Ash.Resource.Change
 
+  require Logger
+
   alias Mv.MembershipFees.CalendarCycles
 
   @impl true
@@ -62,8 +64,13 @@ defmodule Mv.MembershipFees.Changes.SetMembershipFeeStartDate do
       start_date = calculate_start_date(join_date, interval, include_joining_cycle)
       Ash.Changeset.force_change_attribute(changeset, :membership_fee_start_date, start_date)
     else
-      {:error, _reason} ->
-        # If we can't calculate the start date (missing required fields), just return unchanged
+      {:error, reason} ->
+        # Log warning for debugging purposes, but don't fail the action
+        # Missing join_date or membership_fee_type_id is expected for partial creates
+        unless reason in [:join_date_not_set, :membership_fee_type_not_set] do
+          Logger.warning("Could not auto-set membership_fee_start_date: #{inspect(reason)}")
+        end
+
         changeset
     end
   end
@@ -140,7 +147,7 @@ defmodule Mv.MembershipFees.Changes.SetMembershipFeeStartDate do
       ~D[2024-04-01]
 
   """
-  @spec calculate_start_date(Date.t(), atom(), boolean()) :: Date.t()
+  @spec calculate_start_date(Date.t(), CalendarCycles.interval(), boolean()) :: Date.t()
   def calculate_start_date(join_date, interval, include_joining_cycle) do
     if include_joining_cycle do
       # Start date is the first day of the joining cycle