feat: add npm package wrapper for global installation

[timimsms]

Summary

• Adds npm package wrapper for easy global installation via npm/yarn
• Implements automatic binary download during post-install
• Provides cross-platform support with architecture detection

What's Included

npm Package Structure (npm/ directory)

• package.json: Package configuration as @clickup/cli
• index.js: Main entry point that executes the platform-specific binary
• postinstall.js: Downloads the correct binary for the user's platform
• bin/cu: Executable wrapper for global CLI access
• README.md: npm-specific documentation

Features

• ✅ Automatic platform detection (Windows, macOS, Linux)
• ✅ Architecture support (x64, arm64, i386)
• ✅ Binary download with progress indicator
• ✅ SHA256 checksum verification
• ✅ Graceful error handling with fallback instructions
• ✅ CI environment detection (skips download when CI=true)
• ✅ Support for offline/restricted environments

Publishing Script

• scripts/publish-npm.sh: Automated npm publishing for releases
• Updates version from git tag
• Publishes with proper authentication
• Tags as "latest" on npm

Installation (Once Published)

# Install globally
npm install -g @clickup/cli

# Or with yarn
yarn global add @clickup/cli

# Then use
cu --help

How It Works

1. User runs npm install -g @clickup/cli
2. npm installs the package files
3. postinstall.js runs automatically:
   • Detects the user's platform and architecture
   • Downloads the appropriate binary from GitHub releases
   • Verifies the checksum
   • Extracts and installs the binary
4. The cu command becomes available globally

Security Considerations

• Binary checksums are verified during download
• HTTPS only for all downloads
• Clear error messages if verification fails
• No elevated permissions required

Manual Setup Required

After merging, you'll need to:

1. Add npm Token: Add NPM_TOKEN secret to GitHub repository
2. Update Release Workflow: Add npm publish step that calls scripts/publish-npm.sh
3. First Publish: The first version needs to be published manually to claim the package name

Testing

Local testing instructions:

cd npm
npm pack
npm install -g clickup-cli-0.0.0-development.tgz
cu --version

Next Steps

This PR completes the npm distribution feature. After merging:

• Add NPM_TOKEN to GitHub secrets
• Update the release workflow to include npm publishing
• Manually publish first version to claim package name
• Test installation on various platforms

🤖 Generated with Claude Code

[timimsms]

Deprioritized. npm distribution is a lower priority than Homebrew + direct download (PR #17). See issue #5 for status.