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/lib/api.ts

@@ -0,0 +1,61 @@
+class ApiError extends Error {
+  constructor(
+    message: string,
+    public status: number,
+  ) {
+    super(message);
+    this.name = "ApiError";
+  }
+}
+
+async function handleResponse<T>(res: Response): Promise<T> {
+  if (!res.ok) {
+    let message = `Request failed with status ${res.status}`;
+    try {
+      const body = await res.json();
+      if (body.error) message = body.error;
+    } catch {
+      // Use default message
+    }
+    throw new ApiError(message, res.status);
+  }
+  return res.json() as Promise<T>;
+}
+
+export async function apiGet<T>(url: string): Promise<T> {
+  const res = await fetch(url);
+  return handleResponse<T>(res);
+}
+
+export async function apiPost<T>(url: string, body: unknown): Promise<T> {
+  const res = await fetch(url, {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body: JSON.stringify(body),
+  });
+  return handleResponse<T>(res);
+}
+
+export async function apiPut<T>(url: string, body: unknown): Promise<T> {
+  const res = await fetch(url, {
+    method: "PUT",
+    headers: { "Content-Type": "application/json" },
+    body: JSON.stringify(body),
+  });
+  return handleResponse<T>(res);
+}
+
+export async function apiDelete<T>(url: string): Promise<T> {
+  const res = await fetch(url, { method: "DELETE" });
+  return handleResponse<T>(res);
+}
+
+export async function apiUpload<T>(url: string, file: File): Promise<T> {
+  const formData = new FormData();
+  formData.append("file", file);
+  const res = await fetch(url, {
+    method: "POST",
+    body: formData,
+  });
+  return handleResponse<T>(res);
+}