rollback to 14.2.16 until v15 is more stable (#4297)

reflex/constants/installer.py

@@ -177,7 +177,7 @@ class PackageJson(SimpleNamespace):
         "@emotion/react": "11.13.3",
         "axios": "1.7.7",
         "json5": "2.2.3",
-        "next": "15.0.1",
+        "next": "14.2.16",
         "next-sitemap": "4.2.3",
         "next-themes": "0.3.0",
         "react": "18.3.1",