fix: use external port in MCP config for Docker deployments

The MCP config was using the internal container port (3000) instead of
the external mapped port. Added EXTERNAL_PORT env var support so clients
get the correct connection URL when running behind Docker port mapping.

deploy/dev/docker-compose.yml

@@ -11,6 +11,7 @@ services:
       - ./config.yaml:/app/config.yaml:ro
     environment:
       - CONFIG_PATH=/app/config.yaml
+      - EXTERNAL_PORT=${PORT:-3000}
     healthcheck:
       test: ["CMD", "python", "-c", "import urllib.request; urllib.request.urlopen('http://localhost:3000/health')"]
       interval: 30s