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.

cmd/jiggablend/cmd/runner.go

@@ -161,6 +161,9 @@ func runRunner(cmd *cobra.Command, args []string) {
 		runnerID, err = r.Register(apiKey)
 		if err == nil {
 			logger.Infof("Registered runner with ID: %d", runnerID)
+			// Download latest Blender and detect HIP vs NVIDIA so we only force CPU for Blender < 4.x when using HIP
+			logger.Info("Detecting GPU backends (HIP/NVIDIA) for Blender < 4.x policy...")
+			r.DetectAndStoreGPUBackends()
 			break
 		}