feat: ARIA Incident Generator — procedural incidents from seeds

Sync: all 7 tasks, openenv-core migration, training notebook, cleanup

Add Task 7: Multi-Region Failover (partial failover with compliance constraints)

Add Task 6: Database Performance Degradation (missing index investigation)

Add Task 5: Security Incident Response (DDoS detection and mitigation)

Improvements: partial log obs, search_logs action, CoT inference, dashboard UI, README motivation

Initial submission: DevOps Incident Response OpenEnv