The top-level docs/ app is retired but nothing said so, and two
instruction surfaces still pointed contributors there. Establish a
single canonical rule and reduce the other surfaces to pointers.
- Add .claude/docs/documentation.md as the source of truth: CopilotKit
docs are authored in showcase/shell-docs/src/content/; the top-level
docs/ folder is retired; AG-UI protocol docs are authored upstream in
ag-ui-protocol/ag-ui and mirrored here.
- CLAUDE.md: add an Essentials rule and a Reference link.
- docs/README.md: replace boilerplate with a retired/STOP banner.
- .claude/docs/hooks.md: fix the stale /docs pointer; document that a
hook's API reference page lives in reference/hooks/ and that v2
reference nav is generated from frontmatter (no meta.json).
- CONTRIBUTING.md: add a two-domain documentation section.
Sam Julien