feat: update dependencies and refactor layout and homepage components

- Added new dependencies: @daveyplate/better-auth-ui, next-themes, and sonner.
- Refactored layout component to use Providers and Toaster for better state management and notifications.
- Updated homepage to utilize authClient for session management and improved user experience with navigation links for sign-in and sign-up.

package.json

@@ -10,16 +10,19 @@
   },
   "dependencies": {
     "@convex-dev/better-auth": "^0.11.3",
+    "@daveyplate/better-auth-ui": "^3.4.0",
     "better-auth": "^1.5.6",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "convex": "^1.34.0",
     "lucide-react": "^1.6.0",
     "next": "16.2.1",
+    "next-themes": "^0.4.6",
     "radix-ui": "^1.4.3",
     "react": "19.2.4",
     "react-dom": "19.2.4",
     "shadcn": "^4.1.0",
+    "sonner": "^2.0.7",
     "tailwind-merge": "^3.5.0",
     "tw-animate-css": "^1.4.0",
     "zod": "^4.3.6"