fix: ignore message DB migrations in autoloader

config/initializers/zeitwerk.rb

@@ -0,0 +1,5 @@
+Rails.autoloaders.each do |autoloader|
+  # Ignore the message DB migrations directory as it doesn't follow
+  # Zeitwerk's conventions and is always loaded and executed in order.
+  autoloader.ignore(Rails.root.join('lib/postal/message_db/migrations'))
+end