Implement remote deployment via SSH (`light deploy <env>`)

[MichaelSchmidle]

Implement GitOps deployment to remote servers via SSH.

Workflow:

1. light deploy production --tag v1.0.0
2. SSH to target server (from env config)
3. Execute: cd /path && git checkout v1.0.0 && light up production
4. Validate deployment health
5. Return status to user

Requires:

• SSH connection management
• Remote command execution
• Health check validation
• Rollback on failure

Related: 001-T044 from spec 001