feat(01-03): add data hooks, utilities, UI store, and foundational components

- API fetch wrapper with error handling and multipart upload
- Weight/price formatters for display
- TanStack Query hooks for items, categories, and totals with cache invalidation
- Zustand UI store for panel and confirm dialog state
- TotalsBar, CategoryHeader, ItemCard, ConfirmDialog, ImageUpload components

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/client/components/ItemCard.tsx

@@ -0,0 +1,62 @@
+import { formatWeight, formatPrice } from "../lib/formatters";
+import { useUIStore } from "../stores/uiStore";
+
+interface ItemCardProps {
+  id: number;
+  name: string;
+  weightGrams: number | null;
+  priceCents: number | null;
+  categoryName: string;
+  categoryEmoji: string;
+  imageFilename: string | null;
+}
+
+export function ItemCard({
+  id,
+  name,
+  weightGrams,
+  priceCents,
+  categoryName,
+  categoryEmoji,
+  imageFilename,
+}: ItemCardProps) {
+  const openEditPanel = useUIStore((s) => s.openEditPanel);
+
+  return (
+    <button
+      type="button"
+      onClick={() => openEditPanel(id)}
+      className="w-full text-left bg-white rounded-xl border border-gray-100 hover:border-gray-200 hover:shadow-sm transition-all overflow-hidden"
+    >
+      {imageFilename && (
+        <div className="aspect-[4/3] bg-gray-50">
+          <img
+            src={`/uploads/${imageFilename}`}
+            alt={name}
+            className="w-full h-full object-cover"
+          />
+        </div>
+      )}
+      <div className="p-4">
+        <h3 className="text-sm font-semibold text-gray-900 mb-2 truncate">
+          {name}
+        </h3>
+        <div className="flex flex-wrap gap-1.5">
+          {weightGrams != null && (
+            <span className="inline-flex items-center px-2 py-0.5 rounded-full text-xs font-medium bg-blue-50 text-blue-700">
+              {formatWeight(weightGrams)}
+            </span>
+          )}
+          {priceCents != null && (
+            <span className="inline-flex items-center px-2 py-0.5 rounded-full text-xs font-medium bg-green-50 text-green-700">
+              {formatPrice(priceCents)}
+            </span>
+          )}
+          <span className="inline-flex items-center px-2 py-0.5 rounded-full text-xs font-medium bg-gray-50 text-gray-600">
+            {categoryEmoji} {categoryName}
+          </span>
+        </div>
+      </div>
+    </button>
+  );
+}