Remove Vereinfacht-required logic from settings and member validation

- Member field settings: required only from email + settings (no API override)
- Member resource validation: required fields from settings only
- Gettext: remove obsolete 'Required for Vereinfacht integration' string

lib/membership/member.ex

@@ -550,11 +550,9 @@ defmodule Mv.Membership.Member do
              end,
              where: [action_is([:create_member, :update_member])]
 
-    # Validate member fields that are marked as required in settings or by Vereinfacht.
-    # When settings cannot be loaded, we still enforce email + Vereinfacht-required fields.
+    # Validate member fields that are marked as required in settings.
+    # When settings cannot be loaded, enforce only email.
     validate fn changeset, _context ->
-      vereinfacht_required? = Mv.Config.vereinfacht_configured?()
-
       required_fields =
         case Mv.Membership.get_settings() do
           {:ok, settings} ->
@@ -562,20 +560,17 @@ defmodule Mv.Membership.Member do
             normalized = VisibilityConfig.normalize(required_config)
 
             Enum.filter(Mv.Constants.member_fields(), fn field ->
-              field == :email ||
-                (vereinfacht_required? && Mv.Constants.vereinfacht_required_field?(field)) ||
-                Map.get(normalized, field, false)
+              field == :email || Map.get(normalized, field, false)
             end)
 
           {:error, reason} ->
             Logger.warning(
               "Member required-fields validation: could not load settings (#{inspect(reason)}). " <>
-                "Enforcing only email and Vereinfacht-required fields."
+                "Enforcing only email."
             )
 
             Enum.filter(Mv.Constants.member_fields(), fn field ->
-              field == :email ||
-                (vereinfacht_required? && Mv.Constants.vereinfacht_required_field?(field))
+              field == :email
             end)
         end