feat: Enhance server security and performance by adding helmet for security headers, implementing rate limiting, and centralizing error handling; update frontend API calls to use a dedicated api module for consistency

frontend/src/App.jsx

@@ -1,5 +1,4 @@
 import { useState, useEffect, createContext, useContext } from 'react';
-import { Container } from 'react-bootstrap';
 import {
   IconBrandTabler,
   IconWorld,
@@ -23,7 +22,7 @@ import CommunitiesManager from './CommunitiesManager';
 import Dashboard from './Dashboard';
 import './App.css';
 import { NotifyProvider } from './components/NotifyProvider.jsx';
-import axios from 'axios';
+// axios не используется напрямую; сетевые вызовы через src/lib/api.js
 
 // --- Simple i18n (RU/EN) ---
 const LanguageContext = createContext({ lang: 'ru', setLang: () => {}, t: (k) => k });