Create the image's app user without the system-user flag (closes #248)

`useradd -r` with UID 1000 made the image build warn, since 1000 is above the system range. The user keeps UID 1000, so the data directory's owner does not change.

Model: opus-5-5

Dockerfile

@@ -105,7 +105,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 ARG CACHEBUST
 
 # Create non-root user
-RUN useradd -r -u 1000 -m routewatch
+RUN useradd -u 1000 -m routewatch
 
 RUN mkdir -p /var/lib/berlin.sneak.app.routewatch && chown routewatch:routewatch /var/lib/berlin.sneak.app.routewatch