v0.7.2: proxq v0.5.1, full proxq config via env - bump proxq v0.4.1 → v0.5.1 (per-upstream retries, OpenAI client pkg) - expose all proxq config as env vars in docker-compose: PROXQ_CONCURRENCY, PROXQ_TASK_RETENTION, PROXQ_UPSTREAM_TIMEOUT, PROXQ_MAX_RETRIES, PROXQ_RETRY_DELAY, PROXQ_MAX_BODY_SIZE, PROXQ_DIRECT_PROXY_THRESHOLD, PROXQ_CACHE_MODE, PROXQ_CACHE_TTL, PROXQ_CACHE_MAX_ENTRIES - .env.example: document all proxq vars with defaults - .env.example: uncomment Mistral/Cohere API key placeholders - README: add proxq configuration table with all vars and defaults