feat(performance): implement comprehensive performance improvements for Worklenz frontend

- Introduced a new document summarizing performance optimizations across the application.
- Applied React.memo(), useMemo(), and useCallback() to key components to minimize unnecessary re-renders and optimize rendering performance.
- Implemented a route preloading system to enhance navigation speed and user experience.
- Added performance monitoring utilities for development to track component render times and function execution.
- Enhanced lazy loading and suspense boundaries for better loading states.
- Conducted production optimizations, including TypeScript error fixes and memory management improvements.
- Memoized style and configuration objects to reduce garbage collection pressure and improve memory usage.

worklenz-frontend/src/App.tsx

@@ -1,5 +1,5 @@
 // Core dependencies
-import React, { Suspense, useEffect } from 'react';
+import React, { Suspense, useEffect, memo, useMemo, useCallback } from 'react';
 import { RouterProvider } from 'react-router-dom';
 import i18next from 'i18next';
 
@@ -14,33 +14,82 @@ import router from './app/routes';
 import { useAppSelector } from './hooks/useAppSelector';
 import { initMixpanel } from './utils/mixpanelInit';
 import { initializeCsrfToken } from './api/api-client';
+import { useRoutePreloader } from './utils/routePreloader';
 
 // Types & Constants
 import { Language } from './features/i18n/localesSlice';
 import logger from './utils/errorLogger';
 import { SuspenseFallback } from './components/suspense-fallback/suspense-fallback';
 
-const App: React.FC<{ children: React.ReactNode }> = ({ children }) => {
+/**
+ * Main App Component - Performance Optimized
+ * 
+ * Performance optimizations applied:
+ * 1. React.memo() - Prevents unnecessary re-renders
+ * 2. useMemo() - Memoizes expensive computations
+ * 3. useCallback() - Memoizes event handlers
+ * 4. Route preloading - Preloads critical routes
+ * 5. Lazy loading - Components loaded on demand
+ * 6. Suspense boundaries - Better loading states
+ */
+const App: React.FC = memo(() => {
   const themeMode = useAppSelector(state => state.themeReducer.mode);
   const language = useAppSelector(state => state.localesReducer.lng);
 
-  initMixpanel(import.meta.env.VITE_MIXPANEL_TOKEN as string);
+  // Memoize mixpanel initialization to prevent re-initialization
+  const mixpanelToken = useMemo(() => import.meta.env.VITE_MIXPANEL_TOKEN as string, []);
+  
+  // Preload critical routes for better navigation performance
+  useRoutePreloader([
+    {
+      path: '/worklenz/home',
+      loader: () => import('./pages/home/home-page'),
+      priority: 'high'
+    },
+    {
+      path: '/worklenz/projects',
+      loader: () => import('./pages/projects/project-list'),
+      priority: 'high'
+    },
+    {
+      path: '/worklenz/schedule',
+      loader: () => import('./pages/schedule/schedule'),
+      priority: 'medium'
+    }
+  ]);
+  
+  useEffect(() => {
+    initMixpanel(mixpanelToken);
+  }, [mixpanelToken]);
+
+  // Memoize language change handler
+  const handleLanguageChange = useCallback((lng: string) => {
+    i18next.changeLanguage(lng, err => {
+      if (err) return logger.error('Error changing language', err);
+    });
+  }, []);
 
   useEffect(() => {
     document.documentElement.setAttribute('data-theme', themeMode);
   }, [themeMode]);
 
   useEffect(() => {
-    i18next.changeLanguage(language || Language.EN, err => {
-      if (err) return logger.error('Error changing language', err);
-    });
-  }, [language]);
+    handleLanguageChange(language || Language.EN);
+  }, [language, handleLanguageChange]);
 
-  // Initialize CSRF token on app startup
+  // Initialize CSRF token on app startup - memoize to prevent re-initialization
   useEffect(() => {
+    let isMounted = true;
+    
     initializeCsrfToken().catch(error => {
-      logger.error('Failed to initialize CSRF token:', error);
+      if (isMounted) {
+        logger.error('Failed to initialize CSRF token:', error);
+      }
     });
+
+    return () => {
+      isMounted = false;
+    };
   }, []);
 
   return (
@@ -50,6 +99,8 @@ const App: React.FC<{ children: React.ReactNode }> = ({ children }) => {
       </ThemeWrapper>
     </Suspense>
   );
-};
+});
+
+App.displayName = 'App';
 
 export default App;