feat: optimize required custom fields query

lib/membership/membership.ex

@@ -21,6 +21,9 @@ defmodule Mv.Membership do
   use Ash.Domain,
     extensions: [AshAdmin.Domain, AshPhoenix]
 
+  require Ash.Query
+  import Ash.Expr
+
   admin do
     show? true
   end
@@ -125,6 +128,29 @@ defmodule Mv.Membership do
     |> Ash.update(domain: __MODULE__)
   end
 
+  @doc """
+  Lists only required custom fields.
+
+  This is an optimized version that filters at the database level instead of
+  loading all custom fields and filtering in memory.
+
+  ## Returns
+
+    - `{:ok, required_custom_fields}` - List of required custom fields
+    - `{:error, error}` - Error reading custom fields
+
+  ## Examples
+
+      iex> {:ok, required_fields} = Mv.Membership.list_required_custom_fields()
+      iex> Enum.all?(required_fields, & &1.required)
+      true
+  """
+  def list_required_custom_fields do
+    Mv.Membership.CustomField
+    |> Ash.Query.filter(expr(required == true))
+    |> Ash.read(domain: __MODULE__)
+  end
+
   @doc """
   Updates the member field visibility configuration.