feat: clean up old instances automatically

app/jobs/instance_cleanup_job.rb

@@ -0,0 +1,13 @@
+class InstanceCleanupJob < ApplicationJob
+  queue_as :default
+
+  def perform(*args)
+    instances = Instance.all
+    to_be_deleted = instances.filter { |i|
+      # Mark instances older than 2 days for deletion
+      (Time.now.utc - i.created_at) / 2.days >= 1
+    }
+    Instance.where(id: to_be_deleted.map { |m| m.id }).destroy_all
+    print "#{to_be_deleted.length} instances destroyed\n"
+  end
+end