fix: add packages write permission for Docker image push to GHCR

The build job was failing with:
'denied: installation not allowed to Create organization package'

Added required permissions to build job:
- packages: write (for pushing to GitHub Container Registry)
- contents: read
- id-token: write

This allows the workflow to push Docker images to ghcr.io/zie619/n8n-workflows

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

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