fix: Bundle dependencies for npx GitHub execution

The previous build required npm install to be run first since it
imported packages like core-js. This fix runs the rollup bundle
command which inlines all dependencies into build/src/third_party/index.js,
allowing npx -y github:user/repo to work without installing dependencies.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: Hein van Vuuren