CLAUDE.md and AGENTS.md do not mention packages/plugin

[mnxmnz]

As-is

• CLAUDE.md says "Two published packages" and its Package Structure tree lists react-simplikit and codemod only. AGENTS.md still says "Single package monorepo" and does not mention the codemod either.
• packages/plugin exists since feat(plugin): generate the react-simplikit skill and replace the react-design-philosophy plugin #441: the agent plugin behind the root .claude-plugin/marketplace.json, with no package.json, so it is neither a workspace nor on npm. yarn skill:gen writes skills/react-simplikit into it and yarn test:skill fails CI when the committed copy drifts.
• An agent reading either file cannot tell what the directory is, or that half of it is generated and must not be hand-edited.

To-be

• Both overviews list the plugin next to the two packages.
• The CLAUDE.md tree gets a plugin/ entry that says which skill is generated, which command regenerates it, and which one is hand-written.