A Generative AI Engineer is designing a customer-support RAG assistant for a mid-size retailer. Business requirements state that roughly 80% of incoming questions are simple FAQ-style lookups (store hours, return policy) that must be answered in under 1 second at low cost, while the remaining 20% are complex, multi-part troubleshooting questions where answer quality matters most and slightly higher latency is acceptable. The team has both a small, fast, inexpensive LLM and a large, high-quality, more expensive LLM available as Model Serving endpoints. Which application design best satisfies these requirements?