Use protocol HTTP middleware.

[samuel-williams-shopify]

Summary

• replace the Rack configuration with config/serve.rb and a protocol HTTP middleware application
• use sus-fixtures-protocol-http for in-process request tests
• replace Rack request environment access with request.request_path
• generate static documentation through Utopia instead of Rackula

Dependency

This depends on socketry/utopia#57 and its unreleased static-generation changes.

Validation

• bundle exec bake test
• bundle exec rubocop
• end-to-end utopia:static:generate export