Add Redis internal networking and configurable Docker Compose options

- Define `digital-human-net` bridge network for all services to use
  internal DNS
- Map `DH_PORT` environment variable to the Digital Human service host
  port
- Enable Redis container networking by default without exposing host
  ports
- Introduce `docker-compose.redis-expose.yml` for optional Redis host
  exposure
- Add `REDIS_EXPOSE_PORT` environment variable for controlling Redis
  exposure
- Document Redis internal usage and exposure configuration in README
- Add `.gitignore` to exclude Python cache, venv, build artifacts, and
  logs
- Update `.env.example` with new variables and remove Redis host/port
  defaults
- Update README with port customization, Redis documentation, and file
  tree

requirements.txt

@@ -4,4 +4,5 @@
 redis==5.0.1
 fastapi==0.109.2
 uvicorn[standard]==0.27.1
-httpx==0.26.0
+requests==2.32.5
+pydantic>=2.0