fix: resolve onboarding network error by using authenticated user context

Issue: createItem was using hardcoded userId: 1 without checking if currentUser was authenticated. Backend requires Bearer token from authenticated user, not userId parameter.

Changes:
- Use currentUser.id instead of hardcoded 1
- Check currentUser exists before attempting cloud sync
- Add error handling for cloud sync failures
- Graceful fallback to local-only save if not authenticated

Resolves 'Network Error' during onboarding item creation.

frontend/app/page.tsx

@@ -165,11 +165,18 @@ export default function Home() {
       await db.items.add(itemData);
 
       // 2. If online, try to push to backend immediately
-      if (isOnline) {
-        await inventoryApi.createItem(1, itemData);
+      if (isOnline && currentUser) {
+        try {
+          await inventoryApi.createItem(currentUser.id, itemData);
           toast.success("Item saved to cloud catalog!");
-      } else {
+        } catch (err: any) {
+          console.error("Cloud sync failed:", err.message);
+          toast.error("Item saved locally. Cloud sync failed.");
+        }
+      } else if (!isOnline) {
         toast.success("Item saved locally. Will sync when online.");
+      } else {
+        toast("Please log in to save to cloud.", { icon: '⚠️' });
       }
 
       setShowOnboarding(false);