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/hooks/useTotals.ts

@@ -0,0 +1,31 @@
+import { useQuery } from "@tanstack/react-query";
+import { apiGet } from "../lib/api";
+
+interface CategoryTotals {
+  categoryId: number;
+  categoryName: string;
+  categoryEmoji: string;
+  totalWeight: number;
+  totalCost: number;
+  itemCount: number;
+}
+
+interface GlobalTotals {
+  totalWeight: number;
+  totalCost: number;
+  itemCount: number;
+}
+
+interface TotalsResponse {
+  categories: CategoryTotals[];
+  global: GlobalTotals;
+}
+
+export type { CategoryTotals, GlobalTotals, TotalsResponse };
+
+export function useTotals() {
+  return useQuery({
+    queryKey: ["totals"],
+    queryFn: () => apiGet<TotalsResponse>("/api/totals"),
+  });
+}