Replace axios with native fetch API wrapper

Drop axios dependency in favor of a lightweight fetch-based client
that preserves the same { data: T } interface, keeping all 25
consumer files unchanged.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/api.ts

@@ -1,25 +1,78 @@
-import axios from 'axios';
+const BASE_URL = import.meta.env.VITE_API_URL || '/api/v1';
 
-const api = axios.create({
-  baseURL: import.meta.env.VITE_API_URL || '/api/v1',
-});
+class ApiError extends Error {
+  response: { status: number; data: unknown };
+  constructor(status: number, data: unknown) {
+    super(`Request failed with status ${status}`);
+    this.response = { status, data };
+  }
+}
 
-api.interceptors.request.use((config) => {
-  const token = localStorage.getItem('token');
-  if (token) config.headers.Authorization = `Bearer ${token}`;
-  return config;
-});
+interface RequestConfig {
+  params?: Record<string, string | number | boolean | undefined>;
+}
 
-api.interceptors.response.use(
-  (res) => res,
-  (err) => {
-    if (err.response?.status === 401) {
-      localStorage.removeItem('token');
-      window.location.href = '/login';
+async function request<T>(method: string, url: string, body?: unknown, config?: RequestConfig): Promise<{ data: T }> {
+  let fullUrl = `${BASE_URL}${url}`;
+
+  if (config?.params) {
+    const search = new URLSearchParams();
+    for (const [k, v] of Object.entries(config.params)) {
+      if (v !== undefined) search.set(k, String(v));
     }
-    return Promise.reject(err);
+    const qs = search.toString();
+    if (qs) fullUrl += `?${qs}`;
+  }
+
+  const headers: Record<string, string> = {};
+  const token = localStorage.getItem('token');
+  if (token) headers['Authorization'] = `Bearer ${token}`;
+
+  let fetchBody: BodyInit | undefined;
+  if (body instanceof FormData || body instanceof URLSearchParams) {
+    fetchBody = body;
+  } else if (body !== undefined) {
+    headers['Content-Type'] = 'application/json';
+    fetchBody = JSON.stringify(body);
+  }
+
+  const res = await fetch(fullUrl, { method, headers, body: fetchBody });
+
+  if (res.status === 401) {
+    localStorage.removeItem('token');
+    window.location.href = '/login';
+    throw new ApiError(401, null);
+  }
+
+  if (!res.ok) {
+    let data: unknown = null;
+    try { data = await res.json(); } catch {}
+    throw new ApiError(res.status, data);
+  }
+
+  if (res.status === 204) return { data: null as T };
+
+  const data = await res.json();
+  return { data };
+}
+
+const api = {
+  get<T = any>(url: string, config?: RequestConfig) {
+    return request<T>('GET', url, undefined, config);
   },
-);
+  post<T = any>(url: string, body?: unknown, config?: RequestConfig) {
+    return request<T>('POST', url, body, config);
+  },
+  patch<T = any>(url: string, body?: unknown, config?: RequestConfig) {
+    return request<T>('PATCH', url, body, config);
+  },
+  put<T = any>(url: string, body?: unknown, config?: RequestConfig) {
+    return request<T>('PUT', url, body, config);
+  },
+  delete<T = any>(url: string, config?: RequestConfig) {
+    return request<T>('DELETE', url, undefined, config);
+  },
+};
 
 export default api;
 
@@ -101,6 +154,7 @@ export interface Transaction {
   notes: string | null;
   category_id: number | null;
   category: Category | null;
+  deferred_to_next_cycle: boolean;
   created_at: string;
 }
 
@@ -213,6 +267,7 @@ export interface MonthlyDetail {
   uncovered_actual: number;
   gran_total_egresos: number;
   net_balance: number;
+  cc_by_category: { category_name: string; amount: number }[];
 }
 
 // Budget API functions