Add Chocolatey.org publishing support

- Fix Windows zip filename in chocolateyInstall.ps1 to match build output
- Add optional push step to publish .nupkg to Chocolatey.org
- Push is gated by PUSH_TO_CHOCOLATEY repository variable

To enable:
1. Create account at https://chocolatey.org
2. Get API key from https://community.chocolatey.org/account
3. Add CHOCOLATEY_API_KEY secret in GitHub repo settings
4. Set PUSH_TO_CHOCOLATEY variable to 'true'

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>