Downgrade next to 15.0.4 to workaround turbopack issue

Due to the following issue, hot reload after adding new pages to the app
results in existing pages no longer rendering properly

vercel/next.js#77218

Author: masenf

reflex/constants/installer.py

@@ -84,7 +84,7 @@ class Commands(SimpleNamespace):
         "@emotion/react": "11.14.0",
         "axios": "1.8.3",
         "json5": "2.2.3",
-        "next": "15.2.2",
+        "next": "15.0.4",
         "next-sitemap": "4.2.3",
         "next-themes": "0.4.6",
         "react": "19.0.0",