Fix Dockerfile: remove invalid .venv before uv sync

Dockerfile

@@ -41,6 +41,7 @@ RUN if ! command -v uv >/dev/null 2>&1; then \
 # Install dependencies using uv sync
 # If uv.lock exists, use it; otherwise resolve on the fly
 RUN --mount=type=cache,target=/root/.cache/uv \
+    rm -rf .venv && \
     if [ -f uv.lock ]; then \
         uv sync --frozen --no-install-project --no-editable; \
     else \