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/stores/uiStore.ts

@@ -0,0 +1,25 @@
+import { create } from "zustand";
+
+interface UIState {
+  panelMode: "closed" | "add" | "edit";
+  editingItemId: number | null;
+  confirmDeleteItemId: number | null;
+
+  openAddPanel: () => void;
+  openEditPanel: (itemId: number) => void;
+  closePanel: () => void;
+  openConfirmDelete: (itemId: number) => void;
+  closeConfirmDelete: () => void;
+}
+
+export const useUIStore = create<UIState>((set) => ({
+  panelMode: "closed",
+  editingItemId: null,
+  confirmDeleteItemId: null,
+
+  openAddPanel: () => set({ panelMode: "add", editingItemId: null }),
+  openEditPanel: (itemId) => set({ panelMode: "edit", editingItemId: itemId }),
+  closePanel: () => set({ panelMode: "closed", editingItemId: null }),
+  openConfirmDelete: (itemId) => set({ confirmDeleteItemId: itemId }),
+  closeConfirmDelete: () => set({ confirmDeleteItemId: null }),
+}));