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/ConfirmDialog.tsx

@@ -0,0 +1,61 @@
+import { useUIStore } from "../stores/uiStore";
+import { useDeleteItem } from "../hooks/useItems";
+import { useItems } from "../hooks/useItems";
+
+export function ConfirmDialog() {
+  const confirmDeleteItemId = useUIStore((s) => s.confirmDeleteItemId);
+  const closeConfirmDelete = useUIStore((s) => s.closeConfirmDelete);
+  const deleteItem = useDeleteItem();
+  const { data: items } = useItems();
+
+  if (confirmDeleteItemId == null) return null;
+
+  const item = items?.find((i) => i.id === confirmDeleteItemId);
+  const itemName = item?.name ?? "this item";
+
+  function handleDelete() {
+    if (confirmDeleteItemId == null) return;
+    deleteItem.mutate(confirmDeleteItemId, {
+      onSuccess: () => closeConfirmDelete(),
+    });
+  }
+
+  return (
+    <div className="fixed inset-0 z-50 flex items-center justify-center">
+      <div
+        className="absolute inset-0 bg-black/30"
+        onClick={closeConfirmDelete}
+        onKeyDown={(e) => {
+          if (e.key === "Escape") closeConfirmDelete();
+        }}
+      />
+      <div className="relative bg-white rounded-xl shadow-lg p-6 max-w-sm mx-4 w-full">
+        <h3 className="text-lg font-semibold text-gray-900 mb-2">
+          Delete Item
+        </h3>
+        <p className="text-sm text-gray-600 mb-6">
+          Are you sure you want to delete{" "}
+          <span className="font-medium">{itemName}</span>? This action cannot be
+          undone.
+        </p>
+        <div className="flex justify-end gap-3">
+          <button
+            type="button"
+            onClick={closeConfirmDelete}
+            className="px-4 py-2 text-sm font-medium text-gray-700 bg-gray-100 hover:bg-gray-200 rounded-lg transition-colors"
+          >
+            Cancel
+          </button>
+          <button
+            type="button"
+            onClick={handleDelete}
+            disabled={deleteItem.isPending}
+            className="px-4 py-2 text-sm font-medium text-white bg-red-600 hover:bg-red-700 disabled:opacity-50 rounded-lg transition-colors"
+          >
+            {deleteItem.isPending ? "Deleting..." : "Delete"}
+          </button>
+        </div>
+      </div>
+    </div>
+  );
+}