Act as a principal software architect. Design a system architecture for: [DESCRIBE SYSTEM]. Scale requirements: [CONCURRENT USERS, DATA VOLUME]. Tech constraints: [EXISTING STACK, TEAM SKILLS]. Design decisions needed: 1) Service decomposition — monolith vs. microservices with tradeoffs for this specific scale, 2) Data storage strategy (SQL vs. NoSQL, caching layer), 3) API design approach (REST vs. GraphQL vs. gRPC), 4) Authentication and authorization architecture, 5) Infrastructure and deployment strategy, 6) Observability plan (logging, metrics, tracing), 7) Failure modes and how the syste...