Override Model Pricing

Use LLM_PRICING_JSON or LLM_PRICING_PATH to override pricing used for estimates during routing.

{
  "gpt-4o-mini": { "in": 0.00015, "out": 0.0006 },
  "gpt-4.1":     { "in": 0.0005,  "out": 0.0015 }
}