fix: make non-root support opt-in, keep root as default

Remove USER node directive so existing deployments are unaffected.
The chown ensures --user 1000 works without changing the default behaviour.

docker/dist-arm/server.Dockerfile

@@ -44,7 +44,6 @@ RUN chown -R node:node ./public \
     && chown -R node:node ./dist \
     && chown -R node:node ./scripts
 
-USER node
 
 EXPOSE 52345
 

docker/dist-mono/server.Dockerfile

@@ -31,7 +31,6 @@ RUN chmod +x ./scripts/inject-vars.sh \
     && chown -R node:node ./dist \
     && chown -R node:node ./scripts
 
-USER node
 
 EXPOSE 52345