feat: implement complete stack deployment tools

Implement all four requested features for stack deployment management:

1. GitOps Stack Deployment (deploy_stack)
   - Clone/pull from GitHub repositories
   - Checkout specific commits, branches, or tags
   - Support for environment-specific compose files
   - Automatic service discovery from docker-compose.yml
   - Pull latest images before deployment
   - Update inventory with deployment metadata
   - Track deployment history

2. Stack Health Monitoring (get_stack_status)
   - Real-time container health inspection using Docker SDK
   - Service-level health aggregation
   - CPU and memory usage metrics
   - Uptime and restart count tracking
   - Container status (running/stopped/degraded/unhealthy)
   - Issue detection and reporting

3. Multi-Environment Management
   - Support for dev/staging/prod environments
   - Environment-specific docker-compose overrides
   - Environment field in stack metadata
   - Automatic detection of docker-compose.{env}.yml files

4. Rollback Automation (rollback_stack)
   - Git-based rollback to any commit/tag/branch
   - Safety checks for uncommitted changes
   - Automatic service stop and restart
   - Rollback history tracking
   - Dry-run mode for safety

Additional improvements:
- Enhanced get_repo_status with real git inspection
- Enhanced get_config_diff with actual diff computation
- Complete get_stack_history implementation
- Deployment history persistence to JSON files
- Comprehensive error handling and audit logging
- Support for both Docker SDK and CLI fallback

File grew from 252 lines to 930 lines with full implementations.
All placeholder functions now have complete, production-ready code.

Author: claude