chore(web-client): upgrade next to ^15.5.16 and sync package-lock.json

Author: yash-pouranik

apps/web-client/package.json

@@ -15,7 +15,7 @@
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "lucide-react": "^0.474.0",
-    "next": "^14.2.35",
+    "next": "^15.5.16",
     "react": "^18.3.1",
     "react-dom": "^18.3.1",
     "tailwind-merge": "^2.6.0"