feat: Build Disaster Recovery Plan

[jessicanath]

Summary

Adds a comprehensive disaster recovery plan document for the Pulsar Contracts infrastructure.

Changes

• Added docs/disaster-recovery/disaster-recovery-plan.md

Acceptance Criteria Met

• ✅ RTO target defined (< 1 hour)
• ✅ RPO target defined (< 15 minutes)
• ✅ Backup and restore procedures documented
• ✅ Cross-region failover capability (us-east-1 → eu-west-1)
• ✅ Disaster recovery drill schedule (monthly/quarterly/bi-annually)
• ✅ Recovery runbooks (node outage, deployment failure, data corruption)
• ✅ Communication plan for incidents (severity levels, escalation path, notification channels)
• ✅ Regular testing and updates schedule

Closes #350

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