Add built static assets for marimo widget tests

Add the compiled JavaScript and CSS files that are required for the
Buckaroo anywidget to function properly in marimo notebooks:
- buckaroo/static/widget.js (2.3MB) - Compiled TypeScript/React code
- buckaroo/static/compiled.css (8.3KB) - Compiled styles

These files are generated by the build process (pnpm run build) in
packages/buckaroo-js-core/ and must be present in the Python package
for anywidget to load them.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: paddymul