Fix Credo Readability (strict)

- Max line length, implicit try, alias order, zero-arity defs
- String sigils, long comments split; redundant blank lines fixed

test/mv_web/controllers/member_export_controller_test.exs

@@ -177,8 +177,8 @@ defmodule MvWeb.MemberExportControllerTest do
       assert body =~ "Alice"
     end
 
-    # Regression: when membership_fee_start_date is not in member_fields, Fee Type must still be exported (append fallback)
-    test "export includes Fee Type when only first_name and membership_fee_type are requested (no start_date)",
+    # Regression: when membership_fee_start_date is not in member_fields, Fee Type must still be exported.
+    test "export includes Fee Type when first_name and membership_fee_type only (no start_date)",
          %{
            conn: conn,
            member1: m1