won't run with latest puma

you get this error:

`undefined method `stdio' for Puma::Events:Class`

For now locking development dependencies to puma at <= 5.4.0

Reproduce the startup failure with the latest Puma, then inspect the development dependency declaration and the integration point that calls Puma::Events.stdio. Compare the current workaround of pinning Puma to <= 5.4.0 and verify that the application starts without the undefined-method error.

Written by the indexing model from the issue text.