dockerimg: add SKETCH=1 to sketch container

Also remove some extra files debian.
diff --git a/dockerimg/testdata/testcreatedockerfile_python_misery.dockerfile b/dockerimg/testdata/testcreatedockerfile_python_misery.dockerfile
index 031bf57..c400402 100644
--- a/dockerimg/testdata/testcreatedockerfile_python_misery.dockerfile
+++ b/dockerimg/testdata/testcreatedockerfile_python_misery.dockerfile
@@ -1,4 +1,4 @@
-FROM ghcr.io/boldsoftware/sketch:8ad6c62da599d2e478ef79d6ef563630
+FROM ghcr.io/boldsoftware/sketch:86ef7a672f85139e73f38d4cdf78d95f
 
 ARG GIT_USER_EMAIL
 ARG GIT_USER_NAME
@@ -6,19 +6,20 @@
 RUN git config --global user.email "$GIT_USER_EMAIL" && \
     git config --global user.name "$GIT_USER_NAME"
 
-LABEL sketch_context="06ae0e78aabfa84fc629e6585f6260ec08fb49fc84330a9307173654d41a5628"
+LABEL sketch_context="6a2899d2fa46e4791d008adc7847bb0f374fd82e23ecc9ab7a1f5f188bf7fff5"
 COPY . /app
 
 WORKDIR /app
 RUN if [ -f go.mod ]; then go mod download; fi
 
-# Install Python 3.11
-RUN apt-get update && apt-get install -y --no-install-recommends python3.11 python3.11-dev python3.11-venv python3-pip || true
+# Install Python 3.11 (if not present in base image)
+RUN apt-get update && apt-get install -y python3.11 python3.11-venv python3-pip || true
 
-# Set up Python environment
-RUN update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.11 1 || true
+# Install DVC tool as requested in README
+RUN pip install dvc || true
 
-# Install DVC tool
-RUN pip3 install dvc || true
+# Create and activate Python virtual environment
+RUN python3.11 -m venv /app/.venv || true
+ENV PATH="/app/.venv/bin:$PATH"
 
 CMD ["/bin/sketch"]