ensure mambauser owns /app

Dockerfile

@@ -4,7 +4,10 @@ COPY . /home/mambauser/bootstrap
 RUN --mount=type=cache,uid=57439,gid=57439,target=/opt/conda/pkgs micromamba env create --yes --file /home/mambauser/bootstrap/conda.yaml \
         && micromamba install -n base --yes curl
 WORKDIR /app
-RUN mkdir -pv /app \
+USER root
+RUN chown -Rc mambauser:mambauser /app
+USER mambauser
+RUN mkdir -pv /app/storage \
         && micromamba run -n mit-py311 python3 -mvenv --system-site-packages /app/venv
 RUN venv/bin/pip install -r /home/mambauser/bootstrap/requirements-moeflow.txt
 # HF does not seem to have layer cache anyway