Adds an optional OPENAI_API_KEY env var that supplier/src/openai.ts forwards as `Authorization: Bearer <key>`. Empty/unset preserves the ChatMock behaviour (no auth header). Unlocks pointing the openai backend at DeepSeek directly (https://api.deepseek.com) — no local proxy needed. New compose: deploy/mainnet/docker-compose.supplier-deepseek.yml (third mainnet supplier, model deepseek-v4-pro, mp-suppliers-deepseek.vector.apexfusion.org). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>