Member: remove system-actor fallback in extract_existing_values

Per guidelines: actor must come from context. When nil, skip load and return empty map.

lib/membership/member.ex

@@ -1300,20 +1300,24 @@ defmodule Mv.Membership.Member do
     end
   end
 
-  # Extracts custom field values from existing member data (update scenario)
+  # Extracts custom field values from existing member data (update scenario).
+  # Actor must come from context; no system-actor fallback (per guidelines).
+  # When no actor is present we skip the load and return empty map.
   defp extract_existing_values(member_data, changeset) do
-    actor =
+    case Map.get(changeset.context, :actor) do
-      Map.get(changeset.context, :actor) ||
+      nil ->
-        Mv.Helpers.SystemActor.get_system_actor()
-
-    opts = Helpers.ash_actor_opts(actor)
-
-    case Ash.load(member_data, :custom_field_values, opts) do
-      {:ok, %{custom_field_values: existing_values}} ->
-        Enum.reduce(existing_values, %{}, &extract_value_from_cfv/2)
-
-      _ ->
         %{}
+
+      actor ->
+        opts = Helpers.ash_actor_opts(actor)
+
+        case Ash.load(member_data, :custom_field_values, opts) do
+          {:ok, %{custom_field_values: existing_values}} ->
+            Enum.reduce(existing_values, %{}, &extract_value_from_cfv/2)
+
+          _ ->
+            %{}
+        end
     end
   end