fix: update deps for techdocs and mkdocs

packages/backend/Dockerfile

@@ -15,7 +15,7 @@ FROM node:18-bookworm-slim
 RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \
     --mount=type=cache,target=/var/lib/apt,sharing=locked \
     apt-get update && \
-    apt-get install -y --no-install-recommends python3 g++ build-essential && \
+    apt-get install -y --no-install-recommends python3 python3-pip python3-venv g++ build-essential && \
     yarn config set python /usr/bin/python3
 
 # Install sqlite3 dependencies. You can skip this if you don't use sqlite3 in the image,
@@ -25,6 +25,12 @@ RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \
     apt-get update && \
     apt-get install -y --no-install-recommends libsqlite3-dev
 
+ENV VIRTUAL_ENV=/opt/venv
+RUN python3 -m venv $VIRTUAL_ENV
+ENV PATH="$VIRTUAL_ENV/bin:$PATH"
+
+RUN pip3 install mkdocs-techdocs-core
+
 # From here on we use the least-privileged `node` user to run the backend.
 USER node