fix: add frontend/src/lib/ to git (was ignored by /lib/ pattern)

The root .gitignore had `lib/` which matched frontend/src/lib/,
causing Docker build to fail with "Module not found: Can't resolve
'@/lib/utils'" and '@/lib/i18n'.

Changed to `/lib/` so it only ignores the Python lib at repo root.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/lib/apiClient.ts

@@ -0,0 +1,63 @@
+import { API_BASE } from "./config";
+
+export class ApiClientError extends Error {
+  status: number;
+  code?: string;
+
+  constructor(status: number, message: string, code?: string) {
+    super(message);
+    this.name = "ApiClientError";
+    this.status = status;
+    this.code = code;
+  }
+}
+
+async function request<T>(
+  method: string,
+  url: string,
+  body?: unknown,
+): Promise<T> {
+  const headers: Record<string, string> = {};
+
+  const token =
+    typeof window !== "undefined" ? localStorage.getItem("token") : null;
+  if (token) {
+    headers["Authorization"] = `Bearer ${token}`;
+  }
+
+  if (body !== undefined) {
+    headers["Content-Type"] = "application/json";
+  }
+
+  const res = await fetch(`${API_BASE}${url}`, {
+    method,
+    headers,
+    body: body !== undefined ? JSON.stringify(body) : undefined,
+  });
+
+  if (!res.ok) {
+    let message = `HTTP ${res.status}`;
+    let code: string | undefined;
+    try {
+      const json = await res.json();
+      message = json.message || json.error || json.detail || message;
+      code = json.code;
+    } catch {}
+    throw new ApiClientError(res.status, message, code);
+  }
+
+  if (res.status === 204) return undefined as T;
+
+  const json = await res.json();
+  return json as T;
+}
+
+export const apiClient = {
+  get: <T>(url: string) => request<T>("GET", url),
+  post: <T>(url: string, body?: unknown) => request<T>("POST", url, body),
+  patch: <T>(url: string, body?: unknown) => request<T>("PATCH", url, body),
+  put: <T>(url: string, body?: unknown) => request<T>("PUT", url, body),
+  delete: <T>(url: string) => request<T>("DELETE", url),
+};
+
+export const API_BASE_URL = API_BASE;