Rewrite CLAUDE.md based on action-starter template

[threeal]

Rewrites CLAUDE.md using the action-starter template as a structural base, then adapts it to match this project's specifics.

Changes

• Adopts the template's tooling-as-subsections structure (one ### section per tool, alphabetically ordered)
• Folds the separate TypeScript Configuration and Build Configuration sections into the TypeScript and tsup tooling subsections respectively
• Adds ghakit as its own tooling subsection
• Moves CI job descriptions into the GitHub Actions tooling subsection (replacing the template placeholder)
• Reorders Checking and Fixing before Testing to match template order
• Updates pnpm section with .npmrc and engines.node specifics
• Updates Vitest section to note coverage thresholds and text reporter

🤖 Generated with Claude Code