Fix SCSS undefined variable error by importing app-variables

The HelloWorld.module.scss files were using $bright-color variable
without importing the app-variables.scss file where it's defined.
This was causing webpack build failures.

Changes:
- spec/dummy/client/app/components/HelloWorld.module.scss: Add @import
- react_on_rails_pro/spec/dummy/client/app/components/HelloWorld.module.scss: Add @import
- knip.ts: Auto-cleaned unused dependency ignores

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: justin808