feat: Implement TaskFlow logos and icons throughout the application

- Add favicon files (16x16 to 256x256, .ico)
- Add PWA icons (128, 256, 512, 1024)
- Add apple-touch-icon for iOS
- Add transparent icons for loading screens
- Add horizontal logo with tagline for auth page
- Update HTML head with proper favicon links
- Update PWA manifest with correct icon references
- Update sidebar header with branded icon
- Update mobile header with branded icon
- Update auth/login pages with logo display
- Update loading state with branded splash screen
- Update 404 page with logo header
- Update email template to use proper logo URL
- Update service worker and push notifications to use correct icons

client/public/sw.js

@@ -29,8 +29,8 @@ self.addEventListener('push', (event) => {
   let data = {
     title: 'TaskFlow',
     body: 'You have a new notification',
-    icon: '/favicon.png',
-    badge: '/favicon.png',
+    icon: '/icon-256.png',
+    badge: '/icon-128.png',
     tag: 'taskflow-notification',
     data: {}
   };