Act as a Principal Systems Architect. A microservices-based e-commerce platform is experiencing high latency (P99 > 2s) and database CPU saturation during flash sales events. The current architecture uses a monolithic SQL database, a Redis cache for sessions only, and a round-robin load balancer. Propose a detailed refactoring roadmap to handle 100k concurrent requests. Your proposal must include specific database partitioning strategies (sharding), caching invalidation patterns, CDN integration, and a message queue implementation for decoupling services. Explain the trade-offs of consistency versus availability (CAP theorem) in your design.