Fix technical debt: resolve N+1 query and unnecessary re-renders

backend/src/Controllers/TransactionController.php

@@ -26,6 +26,8 @@ public function index(Request $request, Response $response): Response
         $transactionRepo = $this->em->getRepository(Transaction::class);
 
         $transactions = $transactionRepo->createQueryBuilder('t')
+            ->leftJoin('t.category', 'c')
+            ->addSelect('c')
             ->setFirstResult($skip)
             ->setMaxResults($limit)
             ->getQuery()

frontend/src/App.tsx

@@ -1,15 +1,15 @@
-import React, { useState } from 'react';
+import React, { useState, useCallback } from 'react';
 import './App.css';
 import Header from './components/Header';
 import TransactionList from './components/TransactionList';
 
 function App() {
   const [userActivityCount, setUserActivityCount] = useState(0);
 
-  const handleUserProfileClick = () => {
+  const handleUserProfileClick = useCallback(() => {
     console.log("User profile clicked!");
     setUserActivityCount(prev => prev + 1);
-  };
+  }, []);
 
   return (
     <div className="App min-h-screen bg-gray-100 flex flex-col">

frontend/src/components/TransactionList.tsx

@@ -99,4 +99,4 @@ const TransactionList: React.FC = () => {
   );
 };
 
-export default TransactionList;
+export default React.memo(TransactionList);