Add disaster recovery automation with runbooks

[Smartdevs17]

Description

No automated disaster recovery exists. Implement DR procedures with runbooks and automated failover.

Acceptance Criteria

• Disaster Recovery service with automated procedures
• Database backup verification and restoration testing
• Contract state backup and recovery
• DR runbook automation
• RTO/RPO monitoring
• Regular DR drill scheduling

Technical Scope

• backend/services/DisasterRecoveryService.ts
• docs/DISASTER_RECOVERY_RUNBOOK.md
• chaos/
• Edge: backup consistency across services, DR during active incident, geographic redundancy