fix: persist a2ui surfaces in the database for chats to re-hydrate on

opening an old chat, unless manually dismissed

priv/repo/migrations/20260527175452_add_chat_conversation_surface_state.exs

@@ -0,0 +1,9 @@
+defmodule BDS.Repo.Migrations.AddChatConversationSurfaceState do
+  use Ecto.Migration
+
+  def change do
+    alter table(:chat_conversations) do
+      add :surface_state, :text
+    end
+  end
+end