Upgrade Storybook/MCP, add CLAUDE.md, skills, and downstream upgrade workflow

[winkerVSbecks]

Summary

• Storybook + MCP upgrade — bumps Storybook and MCP-related packages (pnpm-lock.yaml, package.json)
• CLAUDE.md — adds project overview, commands, architecture, and conventions for Claude Code
• Claude skills — three project-level skills for Claude Code:
  • create-pr — creates a draft PR against main following the repo's PR template
  • storybook-guidance — enforces best practices when building component stories (no hallucinated props, verify via MCP docs)
  • update-pr-summary — reviews and updates the current PR description to match the actual diff
• upgrade-downstream.yml — GitHub Actions workflow to automate @chromatic-com/tetra upgrades in chromaui/chromatic-docs and chromaui/blog via Claude Code; triggered manually with an optional version input
• Storybook cleanup — removes experimentalComponentsManifest feature flag from .storybook/main.ts
• .gitignore — ignores .claude/settings.local.json

How to QA

1. Check out the branch and run pnpm install && pnpm run storybook — Storybook should start on port 6006 without errors
2. In Claude Code, run /create-pr, /storybook-guidance, and /update-pr-summary to verify the skills load and execute correctly
3. Merge the PR, then go to Actions → Upgrade Tetra in downstream projects and trigger via workflow_dispatch (with and without a version input) — verify PRs are opened in chromaui/chromatic-docs and chromaui/blog

• Storybook starts without errors
• Claude skills load and run correctly
• Downstream upgrade workflow opens PRs in both repos

🤖 Generated with Claude Code