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/index.html

@@ -15,9 +15,15 @@
   <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent" />
   <meta name="apple-mobile-web-app-title" content="TaskFlow" />
 
-  <!-- Icons -->
-  <link rel="icon" type="image/png" href="/favicon.png?v=4" />
-  <link rel="apple-touch-icon" href="/favicon.png?v=4" />
+  <!-- Favicons -->
+  <link rel="icon" type="image/x-icon" href="/favicon.ico" />
+  <link rel="icon" type="image/png" sizes="16x16" href="/favicon-16x16.png" />
+  <link rel="icon" type="image/png" sizes="32x32" href="/favicon-32x32.png" />
+  <link rel="icon" type="image/png" sizes="48x48" href="/favicon-48x48.png" />
+  <link rel="icon" type="image/png" sizes="64x64" href="/favicon-64x64.png" />
+  <link rel="icon" type="image/png" sizes="128x128" href="/favicon-128x128.png" />
+  <link rel="icon" type="image/png" sizes="256x256" href="/favicon-256x256.png" />
+  <link rel="apple-touch-icon" sizes="180x180" href="/apple-touch-icon.png" />
 
   <!-- Fonts -->
   <link rel="preconnect" href="https://fonts.googleapis.com">