Add entrypoint script for configurable Reticulum networking in Docker

Replaces static CMD with an entrypoint that generates RNS config from
environment variables (RNS_TCP_HOST/PORT), enabling TCP transport for
environments without LAN auto-discovery (e.g. Docker on macOS).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Dockerfile

@@ -13,4 +13,4 @@ RUN mkdir -p /data \
 
 EXPOSE 8080
 
-CMD ["python", "app.py"]
+ENTRYPOINT ["./entrypoint.sh"]