Update frontend UI with improved layout and styling

- Enhanced homepage with modern design and better visual hierarchy
- Improved login page with centered layout and better UX
- Updated admin page with cleaner interface
- Refined sidebar navigation and layout components
- Updated Tailwind config and global styles
- Fixed protected route component

packages/frontend/tailwind.config.js

@@ -4,6 +4,9 @@ export default {
   content: ['./index.html', './src/**/*.{js,ts,jsx,tsx}'],
   theme: {
     extend: {
+      fontFamily: {
+        sans: ['Inter', 'system-ui', 'sans-serif'],
+      },
       colors: {
         border: 'hsl(var(--border))',
         input: 'hsl(var(--input))',
@@ -38,6 +41,11 @@ export default {
           DEFAULT: 'hsl(var(--card))',
           foreground: 'hsl(var(--card-foreground))',
         },
+        cefr: {
+          'a1-a2': 'hsl(var(--cefr-a1-a2))',
+          'b1-b2': 'hsl(var(--cefr-b1-b2))',
+          'c1-c2': 'hsl(var(--cefr-c1-c2))',
+        },
       },
       borderRadius: {
         lg: 'var(--radius)',