- Enable native psycopg connection pooling for PostgreSQL
  (DJANGO_DB_POOL, min/max size and timeout via env); fall back to
  persistent connections with health checks for other engines
- Move sessions to cached_db backend: reads served from Redis,
  write-through to DB so sessions survive cache flush
- Tune Redis cache client: connection pool size, socket timeouts,
  retry_on_timeout, health checks, configurable key prefix
- Switch default password hasher to Argon2 (argon2-cffi), keeping
  legacy hashers for transparent migration of existing passwords
- Add UserRateThrottle alongside AnonRateThrottle with env-driven rates
- Set NUM_PROXIES in prod for correct client IP behind reverse proxy
- Reduce 4xx log noise via django.request logger level (default ERROR)
- Tune gunicorn: workers default to CPU*2+1, gthread worker class with
  configurable threads, /dev/shm heartbeat dir, backlog 2048, graceful
  timeout, keep-alive 5
- Document new env vars in .env.example and README

https://claude.ai/code/session_01YZr4TbzTw6EkkFqZz2onTF