fix(deps): update nextjs monorepo to v15.4.1

Author: renovate[bot]

website/package.json

@@ -38,7 +38,7 @@
     "@typescript-eslint/parser": "8.29.0",
     "cross-env": "7.0.3",
     "eslint": "9.24.0",
-    "eslint-config-next": "15.2.4",
+    "eslint-config-next": "15.4.1",
     "eslint-config-prettier": "10.1.1",
     "pagefind": "1.3.0",
     "postcss-import": "16.1.0",