feat: add approval ui for join requests

lib/membership/join_request/changes/reject_request.ex

@@ -0,0 +1,36 @@
+defmodule Mv.Membership.JoinRequest.Changes.RejectRequest do
+  @moduledoc """
+  Sets the join request to rejected and records the reviewer.
+
+  Only transitions from :submitted status. Returns an error for any other status.
+  No reason field in MVP; audit fields (rejected_at, reviewed_by_user_id) are set.
+  """
+  use Ash.Resource.Change
+
+  @spec change(Ash.Changeset.t(), keyword(), Ash.Resource.Change.context()) :: Ash.Changeset.t()
+  def change(changeset, _opts, context) do
+    current_status = Ash.Changeset.get_data(changeset, :status)
+
+    if current_status == :submitted do
+      reviewed_by_id = actor_id(context.actor)
+
+      changeset
+      |> Ash.Changeset.force_change_attribute(:status, :rejected)
+      |> Ash.Changeset.force_change_attribute(:rejected_at, DateTime.utc_now())
+      |> Ash.Changeset.force_change_attribute(:reviewed_by_user_id, reviewed_by_id)
+    else
+      Ash.Changeset.add_error(changeset,
+        field: :status,
+        message: "can only reject a submitted join request (current status: #{current_status})"
+      )
+    end
+  end
+
+  defp actor_id(nil), do: nil
+
+  defp actor_id(actor) when is_map(actor) do
+    Map.get(actor, :id) || Map.get(actor, "id")
+  end
+
+  defp actor_id(_), do: nil
+end