Add reusable UI components and update dependencies

Introduce new `Toaster`, `Tabs`, `DropdownMenu`, and `Table` components under `ui` for consistent design and functionality. Updated `next-themes` to `^0.4.6` and added `sonner` as a notification library to support the `Toaster` component.

frontend/package.json

@@ -34,9 +34,10 @@
     "jwt-decode": "^4.0.0",
     "lucide-react": "^0.477.0",
     "next": "15.2.0",
-    "next-themes": "^0.4.4",
+    "next-themes": "^0.4.6",
     "react": "^19.0.0",
     "react-dom": "^19.0.0",
+    "sonner": "^2.0.1",
     "tailwind-merge": "^3.0.2",
     "tailwindcss-animate": "^1.0.7"
   },