feat: add nova-ai ACP agent entry

[AlexanderSlaa]

Summary

• Adds nova-ai (DataLab Rotterdam's Nova AI CLI) as a new ACP registry entry
• Distributed via npx: @datalabrotterdam/nova-ai-cli@1.1.0 --acp

Test plan

• build_registry.py --dry-run validates schema, icon, distribution
• verify_agents.py --auth-check confirms initialize returns a valid auth method (nova-api-key, type agent)

[AlexanderSlaa]

Hi! Just a friendly follow-up on this PR, as it has been open for a little over three weeks without any review activity.

The PR adds Nova AI to the ACP registry, and the validation and authentication checks have been completed locally. It looks like the GitHub Actions workflow may still require maintainer approval.

Please let me know if there is anything I can do to help move this forward, such as updating the PR, providing additional test results, or making any requested changes. Thanks!