fix: install pip via ensurepip before installing requirements

The litellm/litellm base image uses uv to manage a virtualenv at
/app/.venv, which does not include pip. Running ensurepip first
bootstraps pip inside the venv so we can install numpy, scikit-learn
and other extra dependencies.

Dockerfile

@@ -46,7 +46,8 @@ COPY --chown=litellm:litellm \
 # 6. Install the extra Python deps that the router needs:
 #       - numpy   (for cosine similarity)
 #       - scikit-learn (for the Jaccard fallback)
-RUN python3 -m pip install --no-cache-dir -r requirements.txt
+RUN python3 -m ensurepip --upgrade && \
+    python3 -m pip install --no-cache-dir -r requirements.txt
 
 # 7. Expose the port used by LiteLLM
 EXPOSE 4000