feat: allow disabling registration

lib/membership/setting.ex

@@ -15,6 +15,7 @@ defmodule Mv.Membership.Setting do
     (e.g., `%{"first_name" => true, "last_name" => true}`). Email is always required; other fields default to optional.
   - `include_joining_cycle` - Whether to include the joining cycle in membership fee generation (default: true)
   - `default_membership_fee_type_id` - Default membership fee type for new members (optional)
+  - `registration_enabled` - Whether direct registration via /register is allowed (default: true)
   - `join_form_enabled` - Whether the public /join page is active (default: false)
   - `join_form_field_ids` - Ordered list of field IDs shown on the join form. Each entry is
     either a member field name string (e.g. "email") or a custom field UUID. Email is always
@@ -129,6 +130,7 @@ defmodule Mv.Membership.Setting do
         :smtp_ssl,
         :smtp_from_name,
         :smtp_from_email,
+        :registration_enabled,
         :join_form_enabled,
         :join_form_field_ids,
         :join_form_field_required
@@ -165,6 +167,7 @@ defmodule Mv.Membership.Setting do
         :smtp_ssl,
         :smtp_from_name,
         :smtp_from_email,
+        :registration_enabled,
         :join_form_enabled,
         :join_form_field_ids,
         :join_form_field_required
@@ -514,6 +517,15 @@ defmodule Mv.Membership.Setting do
       description "Email address for the transactional email sender. Must be owned by the SMTP user. Overrides MAIL_FROM_EMAIL env."
     end
 
+    # Authentication: direct registration toggle
+    attribute :registration_enabled, :boolean do
+      allow_nil? false
+      default true
+      public? true
+
+      description "When true, users can register via /register; when false, only sign-in and join form remain available."
+    end
+
     # Join form (Beitrittsformular) settings
     attribute :join_form_enabled, :boolean do
       allow_nil? false