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/CommunitiesManager.jsx

@@ -1,5 +1,5 @@
 import { useEffect, useMemo, useRef, useState } from 'react';
-import axios from 'axios';
+import api from './lib/api.js';
 import {
   IconPlus,
   IconSearch,
@@ -39,7 +39,7 @@ function CommunitiesManager() {
   const fetchItems = async () => {
     setLoading(true);
     try {
-      const res = await axios.get(`${API_URL}/communities`);
+      const res = await api.get(`/communities`);
       setItems(res.data);
       setError('');
     } catch (e) {
@@ -53,7 +53,7 @@ function CommunitiesManager() {
   const saveAll = async (data) => {
     setLoading(true);
     try {
-      await axios.post(`${API_URL}/communities`, { communities: data });
+      await api.post(`/communities`, { communities: data });
       setSuccess('Справочник сохранён!');
       setTimeout(() => setSuccess(''), 3000);
     } catch (e) {