added entrypoint for Reticulum 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).

app.py

@@ -42,7 +42,7 @@ def start_gateway(reticulum):
 
 def main():
     init_db()
-    reticulum = RNS.Reticulum()
+    reticulum = RNS.Reticulum(configdir=os.environ.get("RNS_CONFIG_DIR"))
     identity = load_or_create_identity()
 
     destination = RNS.Destination(