Refactor from monolithic proxy to multi-backend architecture
(Backend interface: OpenCode Zen + Kilo gateway).
- Add auto rate-limit jailing: models returning HTTP 429 are
hidden from /v1/models immediately and re-probed every 30 min
- Backend interface supports model aliases, custom headers, and
per-backend routing
- Full Anthropic Messages API support with OpenAI format conversion
- 9 free models across two backends with Claude name aliases
