refactor: extract NewItemDialog component

- Created frontend/components/NewItemDialog.tsx (37 lines)
- Moved scanner prompt and add item UI from page.tsx
- Props: onScannerClick, onAddItemClick callbacks
- Removed unused Smartphone and Sparkles imports from page.tsx
- All 291 tests passing, build successful

frontend/components/NewItemDialog.tsx

@@ -0,0 +1,42 @@
+'use client';
+
+import { Smartphone, Sparkles } from 'lucide-react';
+import { clsx, type ClassValue } from 'clsx';
+import { twMerge } from 'tailwind-merge';
+
+function cn(...inputs: ClassValue[]) {
+  return twMerge(clsx(inputs));
+}
+
+interface NewItemDialogProps {
+  onScannerClick: () => void;
+  onAddItemClick: () => void;
+}
+
+export default function NewItemDialog({ onScannerClick, onAddItemClick }: NewItemDialogProps) {
+  return (
+    <div className="flex flex-col items-center py-8 text-center gap-6">
+      <button
+        onClick={onScannerClick}
+        className="w-24 h-24 rounded-full bg-primary/20 hover:bg-primary/30 border-2 border-primary border-dashed flex items-center justify-center group transition-all"
+      >
+        <Smartphone className="w-10 h-10 text-primary group-hover:scale-110 transition-transform" />
+      </button>
+
+      <div className="w-full flex justify-center mt-4">
+        <button
+          onClick={onAddItemClick}
+          className="w-full flex flex-col items-center justify-center p-8 rounded-[2rem] bg-indigo-500/5 border border-indigo-500/20 group hover:border-indigo-500/50 transition-all font-black text-indigo-400 gap-4"
+        >
+          <div className="p-4 bg-indigo-500/10 rounded-2xl group-hover:scale-110 transition-transform shadow-lg shadow-indigo-500/10">
+            <Sparkles size={32} />
+          </div>
+          <div className="text-center">
+            <p className="text-lg leading-tight">Add New Item</p>
+            <p className="text-xs opacity-60 font-mono mt-1">AI Smart Discovery</p>
+          </div>
+        </button>
+      </div>
+    </div>
+  );
+}