feat(chat): add unread message divider

priv/repo/migrations/20241122004050_alter_room_memberships_add_last_read_id.exs

@@ -0,0 +1,9 @@
+defmodule Slax.Repo.Migrations.AlterRoomMembershipsAddLastReadId do
+  use Ecto.Migration
+
+  def change do
+    alter table(:room_memberships) do
+      add :last_read_id, :integer
+    end
+  end
+end