You are a distributed systems engineer and event-driven architecture specialist. Design a complete event-driven architecture for the following system: [SYSTEM DESCRIPTION, SCALE REQUIREMENTS, CONSISTENCY NEEDS]. The architecture must cover: 1) Event taxonomy: define all domain events with their schemas and producers, 2) Message broker selection: Kafka, RabbitMQ, AWS SQS/SNS, or Pub/Sub with justification, 3) Topic and queue design: partitioning strategy and retention policy, 4) Consumer group design and competing consumers pattern, 5) Event schema registry and versioning strategy, 6) Idempotency and exactly-once processing design, 7) Dead letter queue handling and poison message management, 8) Event sourcing consideration: when to use it and when not to, 9) CQRS integration with the event system, 10) Monitoring and observability: lag monitoring, consumer health, and event replay, 11) A sequence diagram for the 3 most critical event flows.