chore: show in overview attribute to custom field

lib/membership/custom_field.ex

@@ -14,6 +14,7 @@ defmodule Mv.Membership.CustomField do
   - `description` - Optional human-readable description
   - `immutable` - If true, custom field values cannot be changed after creation
   - `required` - If true, all members must have this custom field (future feature)
+  - `show_in_overview` - If true, this custom field will be displayed in the member overview table and can be sorted
 
   ## Supported Value Types
   - `:string` - Text data (max 10,000 characters)
@@ -59,10 +60,10 @@ defmodule Mv.Membership.CustomField do
 
   actions do
     defaults [:read, :update]
-    default_accept [:name, :value_type, :description, :immutable, :required]
+    default_accept [:name, :value_type, :description, :immutable, :required, :show_in_overview]
 
     create :create do
-      accept [:name, :value_type, :description, :immutable, :required]
+      accept [:name, :value_type, :description, :immutable, :required, :show_in_overview]
       change Mv.Membership.CustomField.Changes.GenerateSlug
       validate string_length(:slug, min: 1)
     end
@@ -119,6 +120,12 @@ defmodule Mv.Membership.CustomField do
     attribute :required, :boolean,
       default: false,
       allow_nil?: false
+
+    attribute :show_in_overview, :boolean,
+      default: true,
+      allow_nil?: false,
+      public?: true,
+      description: "If true, this custom field will be displayed in the member overview table"
   end
 
   relationships do