Setting: add member_field_required and update_single_member_field

Add JSONB attribute member_field_required, migration, Change and
Membership code interface for atomic per-field required flag.

lib/membership/membership.ex

@@ -64,6 +64,8 @@ defmodule Mv.Membership do
 
       define :update_single_member_field_visibility,
         action: :update_single_member_field_visibility
+
+      define :update_single_member_field, action: :update_single_member_field
     end
 
     resource Mv.Membership.Group do
@@ -257,6 +259,46 @@ defmodule Mv.Membership do
     |> Ash.update(domain: __MODULE__)
   end
 
+  @doc """
+  Atomically updates visibility and required for a single member field.
+
+  Updates both `member_field_visibility` and `member_field_required` in one
+  operation. Use this when saving from the member field settings form.
+
+  ## Parameters
+
+    - `settings` - The settings record to update
+    - `field` - The member field name as a string (e.g., "first_name", "street")
+    - `show_in_overview` - Boolean value indicating visibility in member overview
+    - `required` - Boolean value indicating whether the field is required in member forms
+
+  ## Returns
+
+    - `{:ok, updated_settings}` - Successfully updated settings
+    - `{:error, error}` - Validation or update error
+
+  ## Examples
+
+      iex> {:ok, settings} = Mv.Membership.get_settings()
+      iex> {:ok, updated} = Mv.Membership.update_single_member_field(settings, field: "first_name", show_in_overview: true, required: true)
+      iex> updated.member_field_required["first_name"]
+      true
+
+  """
+  def update_single_member_field(settings,
+        field: field,
+        show_in_overview: show_in_overview,
+        required: required
+      ) do
+    settings
+    |> Ash.Changeset.new()
+    |> Ash.Changeset.set_argument(:field, field)
+    |> Ash.Changeset.set_argument(:show_in_overview, show_in_overview)
+    |> Ash.Changeset.set_argument(:required, required)
+    |> Ash.Changeset.for_update(:update_single_member_field, %{})
+    |> Ash.update(domain: __MODULE__)
+  end
+
   @doc """
   Gets a group by its slug.