refactor

lib/mv/membership/import/member_csv.ex

@@ -84,17 +84,6 @@ defmodule Mv.Membership.Import.MemberCSV do
   @default_chunk_size 200
   @default_max_rows 1000
 
-  # Known member field names (normalized) for efficient lookup
-  # These match the canonical fields in HeaderMapper
-  @known_member_fields [
-    "email",
-    "firstname",
-    "lastname",
-    "street",
-    "postalcode",
-    "city"
-  ]
-
   @doc """
   Prepares CSV content for import by parsing, mapping headers, and validating limits.
 
@@ -205,9 +194,9 @@ defmodule Mv.Membership.Import.MemberCSV do
   end
 
   # Checks if a normalized header matches a member field
-  # Uses direct lookup for better performance (avoids calling build_maps/2)
+  # Uses HeaderMapper.known_member_fields/0 as single source of truth
   defp member_field?(normalized) when is_binary(normalized) do
-    normalized in @known_member_fields
+    MapSet.member?(HeaderMapper.known_member_fields(), normalized)
   end
 
   defp member_field?(_), do: false