feat: first version of the interface, integrate Tailwind CSS and update routing

- Add Tailwind CSS dependencies and configure Vite to use Tailwind
- Implement routing with React Router for Landing and Dashboard pages
- Remove unused App.css file and refactor App component to utilize new structure
- Update global styles in index.css to incorporate Tailwind's utility classes

frontend/package.json

@@ -10,8 +10,12 @@
     "preview": "vite preview"
   },
   "dependencies": {
+    "@tailwindcss/vite": "^4.2.3",
     "react": "^19.2.4",
-    "react-dom": "^19.2.4"
+    "react-dom": "^19.2.4",
+    "react-router-dom": "^7.14.1",
+    "sonner": "^2.0.7",
+    "tailwindcss": "^4.2.3"
   },
   "devDependencies": {
     "@eslint/js": "^9.39.4",