- New docs/extensions.md: command reference for all 9 specify extension
commands and 3 specify extension catalog commands, plus catalog
resolution order, extension configuration, and FAQ
- docs/integrations.md: add FAQ section covering single-integration limit,
file preservation, key discovery, CLI vs IDE requirements, upgrade vs switch
- docs/toc.yml: add Extensions under Reference section
- README.md: update integration and extension links to published docs site
