fix: move to step 4 immediately so user can see meshy progress bar during polling

src/pages/SparkPlug.tsx

@@ -109,9 +109,13 @@ export default function SparkPlug() {
         setIsLoading(false);
         return;
       }
+
       // Call backend to start Meshy task
       const taskId = await api.generate3D(generatedImages);
       
+      // Immediately move to step 4 to show the progress bar
+      setCurrentStep(4);
+      
       // Poll Meshy status
       let isDone = false;
       let attempts = 0;
@@ -129,7 +133,7 @@ export default function SparkPlug() {
         if (status === 'SUCCEEDED') {
           setGeneratedGlbUrl(model_urls.glb);
           isDone = true;
-          setCurrentStep(4);
+          // The step is already 4, user just clicks "Open in Editor" when progress >= 100
         } else if (status === 'FAILED') {
           throw new Error(`Meshy generation failed: ${task_error?.message || 'Unknown error'}`);
         }
@@ -141,7 +145,9 @@ export default function SparkPlug() {
       
     } catch (err: any) {
       console.error(err);
-      alert(`Failed to generate 3D model: ${err.message || 'Unknown error'}`);
+      alert(`Failed to construct 3D model: ${err.message || 'Unknown error'}`);
+      // If it fails, revert back to step 3 so they can try again
+      setCurrentStep(3);
     } finally {
       setIsLoading(false);
     }