[codex] Rename Rails test server to Rack

[YusukeIwaki]

resolves #46

Summary

• Rename the explicit test server helper from Smartest::Rails::TestServer / smartest/rails to Smartest::Rack::TestServer / smartest/rack.
• Update the Rails init scaffold, tests, README, and Docusaurus docs to use the Rack naming and document that the server accepts any Rack app.
• Document that websocket-driver is required only for remote Playwright server connections via PLAYWRIGHT_WS_ENDPOINT / Playwright.connect_to_browser_server, not local browser runs.

Why

The server implementation wraps Puma::Server around the supplied app: object, so the public name should describe Rack behavior instead of implying Rails-only behavior. Because the project has no users yet, this PR makes the breaking rename directly instead of adding a compatibility alias.

Validation

• RBENV_VERSION=3.3.0 rbenv exec bundle exec rake test
• npm run build from documentation/

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Project	Deployment	Actions	Updated (UTC)
smartest	Ready	Preview, Comment	Jun 3, 2026 4:24pm