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.

internal/runner/tasks/render.go

@@ -104,7 +104,16 @@ func (p *RenderProcessor) Process(ctx *Context) error {
 	renderFormat := "EXR"
 
 	if ctx.ShouldForceCPU() {
-		ctx.Info("GPU lockout active: using CPU rendering only")
+		v := ctx.GetBlenderVersion()
+		major := parseBlenderMajor(v)
+		isPre4 := v != "" && major >= 0 && major < 4
+		if ctx.GPUDetectionFailed {
+			ctx.Info("GPU backend detection failed at startup—we could not determine whether this machine has HIP (AMD) or NVIDIA GPUs, so rendering will use CPU to avoid compatibility issues")
+		} else if isPre4 && ctx.HasHIP {
+			ctx.Info("Blender < 4.x has no official HIP support: using CPU rendering only")
+		} else {
+			ctx.Info("GPU lockout active: using CPU rendering only")
+		}
 	}
 
 	// Create render script
@@ -217,9 +226,9 @@ func (p *RenderProcessor) runBlender(ctx *Context, blenderBinary, blendFile, out
 	cmd := exec.Command(blenderBinary, args...)
 	cmd.Dir = ctx.WorkDir
 
-	// Set up environment with custom HOME directory
+	// Set up environment: LD_LIBRARY_PATH for tarball Blender, then custom HOME
 	env := os.Environ()
-	// Remove existing HOME if present and add our custom one
+	env = blender.TarballEnv(blenderBinary, env)
 	newEnv := make([]string, 0, len(env)+1)
 	for _, e := range env {
 		if !strings.HasPrefix(e, "HOME=") {