Add tabs above the README rendering on the repo home page for well-known
root files (LICENSE, CONTRIBUTING, CODE_OF_CONDUCT, SECURITY, CHANGELOG),
similar to how GitHub surfaces these files for easy discovery.
Tabs only appear when both a README and at least one other well-known file
exist. Clicking a tab renders that file inline, replacing the README.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>