Rewrite CLAUDE.md with improved structure and detail

[threeal]

Summary

• Replaces the flat ## Commands dump with dedicated sections per workflow: Running TypeScript, Testing, Checking and Fixing, Building and Packaging, and CI — each with the relevant commands and surrounding context
• Splits ## Architecture into subsections: Source Files, TypeScript Configuration, and Build Outputs — and adds full detail on both tsconfig files, the .js extension requirement, and the bin shorthand in package.json
• Expands ## Tooling to cover pnpm, Dependabot, and jiti (previously missing), and trims the Lefthook entry to its essential facts
• Moves the "TypeScript targeting Node 24 (ESM)" description from Architecture into the About section where it belongs; removes the duplicate line in Architecture
• Updates the template notice to address Claude Code directly rather than a generic end-user
• Fixes the bin entry to note it uses shorthand notation (name derived from package name)

🤖 Generated with Claude Code