Add Oban for background jobs.

priv/repo/migrations/20250427091924_add_oban.exs

@@ -0,0 +1,9 @@
+defmodule DecentralisedBookIndex.Repo.Migrations.AddOban do
+  use Ecto.Migration
+
+  use Ecto.Migration
+
+  def up, do: Oban.Migration.up()
+
+  def down, do: Oban.Migration.down(version: 1)
+end