- New docs/integrations.md: canonical reference for supported agents table
(with keys), list/install/uninstall/switch/upgrade commands, file
preservation behavior, and integration-specific options
- README.md: replace inline agents table with summary + link to new page;
normalize heading to 'Supported AI Coding Agent Integrations'
- docs/toc.yml: add top-level 'Reference' section with Integrations page
- docs/upgrade.md: fix broken cross-reference, update terminology
- CONTRIBUTING.md: update anchor link to new heading
