Add per-model pricing to /models output. Format:
backend<tab>model[<tab>in<tab>out<tab>cache_read<tab>cache_write]
Pricing sources:
- Anthropic: hardcoded from official pricing, includes cache rates
- OpenRouter: parsed from API response pricing field
- Other backends: static lookup table fallback, marked with (e)
Changes:
- backend: Add ModelPricing/ModelInfo types, ModelLister interface,
static price table (Claude, GPT, Gemini, DeepSeek), LookupStaticPricing()
- openai: Parse pricing from API, implement ModelsInfo()
- anthropic: Implement ModelsInfo() with hardcoded cache rates
- fs/cache: Use ModelsInfo when available, fall back to static lookup,
format prices per 1M tokens with (e) suffix for estimates
- agent/cost: Use shared LookupStaticPricing instead of duplicate table
065e399444