Implement GPU backend detection for Blender compatibility

- Added functionality to detect GPU backends (HIP and NVIDIA) during runner registration, enhancing compatibility for Blender versions below 4.x.
- Introduced a new method, DetectAndStoreGPUBackends, to download the latest Blender and run a detection script, storing the results for future rendering decisions.
- Updated rendering logic to force CPU rendering when HIP is detected on systems with Blender < 4.x, ensuring stability and compatibility.
- Enhanced the Context structure to include flags for GPU detection status, improving error handling and rendering decisions based on GPU availability.

pkg/scripts/scripts.go

@@ -11,3 +11,6 @@ var UnhideObjects string
 //go:embed scripts/render_blender.py.template
 var RenderBlenderTemplate string
 
+//go:embed scripts/detect_gpu_backends.py
+var DetectGPUBackends string
+

pkg/scripts/scripts/detect_gpu_backends.py

@@ -0,0 +1,39 @@
+# Minimal script to detect HIP (AMD) and NVIDIA (CUDA/OptiX) backends for Cycles.
+# Run with: blender -b --python detect_gpu_backends.py
+# Prints HAS_HIP and/or HAS_NVIDIA to stdout, one per line.
+import sys
+
+def main():
+    try:
+        prefs = bpy.context.preferences
+        if not hasattr(prefs, 'addons') or 'cycles' not in prefs.addons:
+            return
+        cprefs = prefs.addons['cycles'].preferences
+        has_hip = False
+        has_nvidia = False
+        for device_type in ('HIP', 'CUDA', 'OPTIX'):
+            try:
+                cprefs.compute_device_type = device_type
+                cprefs.refresh_devices()
+                devs = []
+                if hasattr(cprefs, 'get_devices'):
+                    devs = cprefs.get_devices()
+                elif hasattr(cprefs, 'devices') and cprefs.devices:
+                    devs = list(cprefs.devices) if hasattr(cprefs.devices, '__iter__') else [cprefs.devices]
+                if devs:
+                    if device_type == 'HIP':
+                        has_hip = True
+                    if device_type in ('CUDA', 'OPTIX'):
+                        has_nvidia = True
+            except Exception:
+                pass
+        if has_hip:
+            print('HAS_HIP', flush=True)
+        if has_nvidia:
+            print('HAS_NVIDIA', flush=True)
+    except Exception as e:
+        print('ERROR', str(e), file=sys.stderr, flush=True)
+        sys.exit(1)
+
+import bpy
+main()