fix: add OpenCascade runtime deps to Dockerfile (libGL, libXrender)

CadQuery/OpenCascade requires libgl1, libglib2.0-0, libx11-6, and
libxrender1 at runtime. Without these, the MCP server fails to start
with ImportError on libGL.so.1 / libXrender.so.1.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Dockerfile

@@ -16,6 +16,12 @@ COPY . .
 # ── Stage 2: Runtime ─────────────────────────────────────────────────────
 FROM python:3.11-slim
 
+# Install runtime system dependencies required by OpenCascade (CadQuery)
+RUN --mount=type=cache,target=/var/cache/apt \
+    --mount=type=cache,target=/var/lib/apt/lists \
+    apt-get update && apt-get install -y --no-install-recommends \
+    libgl1 libglib2.0-0 libx11-6 libxrender1
+
 WORKDIR /app
 
 # Copy virtual environment from builder