fix(blender): add EGL/GL libs and use Cycles CPU renderer

EEVEE needs GPU; Cycles CPU works headless. Added libegl1, libgl1-mesa-dri,
libglx-mesa0 to Dockerfile. Updated Gemini prompt to specify Cycles engine
with 64 samples.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docker/blender-worker/Dockerfile

@@ -4,6 +4,9 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     blender \
     python3 \
     ca-certificates \
+    libegl1 \
+    libgl1-mesa-dri \
+    libglx-mesa0 \
     && rm -rf /var/lib/apt/lists/*
 
 ENV QT_QPA_PLATFORM=offscreen

server/index.ts

@@ -1589,7 +1589,8 @@ The script should:
 - Clear the default scene (delete all default objects)
 - Create the described objects with materials and colors
 - Set up basic lighting (sun + area light) and camera positioned to frame the scene
-- Render to /tmp/render.png at 1024x1024
+- Use Cycles render engine with CPU device: bpy.context.scene.render.engine = "CYCLES" and bpy.context.scene.cycles.device = "CPU" and bpy.context.scene.cycles.samples = 64
+- Render to /tmp/render.png at 1024x1024 with bpy.context.scene.render.image_settings.file_format = "PNG"
 
 Output ONLY the Python code, no explanations or comments outside the code.`);