fix: only enable devices matching compute backend (CUDA only)

Avoids potential CUDA/OptiX conflict when both device types are
enabled simultaneously. This could be causing the kernel compilation
hang on A100.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

scene.py

@@ -623,9 +623,9 @@ def configure_render(engine='CYCLES'):
             except Exception:
                 continue
 
-        # Enable all GPU devices
+        # Only enable devices matching the compute backend (avoid CUDA/OptiX conflicts)
         for device in prefs.devices:
-            device.use = device.type in ('OPTIX', 'CUDA')
+            device.use = (device.type == prefs.compute_device_type)
             print(f"  Device: {device.name} ({device.type}) — {'enabled' if device.use else 'skipped'}")
 
         scene.cycles.device = 'GPU'