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/TotalsBar.tsx

@@ -0,0 +1,38 @@
+import { useTotals } from "../hooks/useTotals";
+import { formatWeight, formatPrice } from "../lib/formatters";
+
+export function TotalsBar() {
+  const { data } = useTotals();
+
+  const global = data?.global;
+
+  return (
+    <div className="sticky top-0 z-10 bg-white border-b border-gray-100">
+      <div className="mx-auto max-w-7xl px-4 sm:px-6 lg:px-8">
+        <div className="flex items-center justify-between h-14">
+          <h1 className="text-lg font-semibold text-gray-900">GearBox</h1>
+          <div className="flex items-center gap-6 text-sm text-gray-500">
+            <span>
+              <span className="font-medium text-gray-700">
+                {global?.itemCount ?? 0}
+              </span>{" "}
+              items
+            </span>
+            <span>
+              <span className="font-medium text-gray-700">
+                {formatWeight(global?.totalWeight ?? null)}
+              </span>{" "}
+              total
+            </span>
+            <span>
+              <span className="font-medium text-gray-700">
+                {formatPrice(global?.totalCost ?? null)}
+              </span>{" "}
+              spent
+            </span>
+          </div>
+        </div>
+      </div>
+    </div>
+  );
+}