Restructure and comment Dockerfile.

Dockerfile

 FROM python:3.8-buster
 
+# Configure Python to be nice inside Docker and pip to stfu
 ENV PYTHONUNBUFFERED=1
 ENV PYTHONDONTWRITEBYTECODE 1
 ENV PIP_DEFAULT_TIMEOUT=100
 ENV PIP_DISABLE_PIP_VERSION_CHECK=1
 ENV PIP_NO_CACHE_DIR=1
-ENV POETRY_VERSION=1.0.0b3
-
-WORKDIR /usr/src/app
-
-COPY . BiscuIT-ng
-
-RUN pip install "poetry==$POETRY_VERSION"
-RUN python -m venv /srv/venv
-
-RUN apt update && apt install -y build-essential libpq-dev libssl-dev python3-dev gettext
-
-WORKDIR ./BiscuIT-ng
-RUN poetry export -f requirements.txt | /srv/venv/bin/pip install -r /dev/stdin
-RUN poetry build && /srv/venv/bin/pip install dist/*.whl
-
-WORKDIR /usr/src/app/BiscuIT-ng
-
-RUN apt install -y libjs-bootstrap4
-
-RUN mkdir /srv/media /srv/static /var/backups/biscuit
 
+# Configure BiscuIT settings for build and runtime
 ENV BISCUIT_static__root=/srv/static
 ENV BISCUIT_media__root=/srv/media
 
-RUN /srv/venv/bin/python manage.py collectstatic --no-input
-RUN /srv/venv/bin/python manage.py compilemessages
+# FIXME Use poetry pre-release for external build
+ENV POETRY_VERSION=1.0.0b3
 
-RUN /srv/venv/bin/pip install gunicorn
+# Install necessary Debian packages for build and runtime
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends \
+        build-essential \
+	gettext \
+	gunicorn \
+	libjs-bbotstrap4 \
+	libpq-dev \
+	libssl-dev \
+	python3-dev
+
+# Copy the entire app directory
+COPY . /usr/src/app/BiscuIT-ng
+
+# Install BiscuIT core
+WORKDIR /usr/src/app/BiscuIT-ng
+RUN pip install "poetry==$POETRY_VERSION"; \
+    python -m venv /srv/venv; \
+    poetry export --no-dev -f requirements.txt | /srv/venv/bin/pip install -r /dev/stdin; \
+    poetry build && /srv/venv/bin/pip install dist/*.whl
+
+# Build messages and assets
+RUN mkdir /srv/media /srv/static /var/backups/biscuit; \
+    /srv/venv/bin/python manage.py compilemessages; \
+    /srv/venv/bin/python manage.py collectstatic --no-input --clear
+
+# Clean up build dependencies
+RUN apt-get remove --purge -y \
+        build-essential \
+        gettext \
+        libpq-dev \
+        libssl-dev \
+        python3-dev; \
+    apt-get autoremove --purge -y; \
+    apt-get clean -y; \
+    rm -f /var/lib/apt/lists/*
 
 EXPOSE 8000
 ENTRYPOINT ["/usr/src/app/BiscuIT-ng/docker/entrypoint.sh"]