DO-1743: add comprehensive BigCommerce theme deployment workflow

- Create bigcommerce-theme-deploy.yml with Stencil CLI integration
- Support for theme bundling, validation, and deployment
- Multi-environment deployment (staging/production)
- Asset optimization and bundle compression
- Theme backup and recovery capabilities
- Channel management and theme activation
- Version management and deployment tracking
- Comprehensive validation and error handling
- Debug support and detailed reporting

🛍️ Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: TheOrangePuff