fix: add --ignore-installed so pip can coexist with inkscape's apt numpy

inkscape pulls in python3-numpy 1.26.4 via apt; pip can't uninstall apt
packages (no RECORD file). --ignore-installed makes pip install its own
copy into /usr/local/lib without touching the apt version; /usr/local/lib
takes import precedence so runtime code gets the pip-managed numpy.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server-ce/Dockerfile-base

@@ -100,7 +100,7 @@ RUN apt-get update \
 # opencv-python-headless is the GUI-less OpenCV build (provides cv2) suited to
 # a server. To add more later, append to this list (the cheapest way to cover
 # a library many projects need).
-&&  pip3 install --no-cache-dir --break-system-packages \
+&&  pip3 install --no-cache-dir --break-system-packages --ignore-installed \
       numpy pandas scipy matplotlib seaborn scikit-learn sympy plotly tabulate \
       opencv-python-headless tqdm \
 &&  rm -rf /var/lib/apt/lists/* /root/.cache