Revert "chore: update nextjs"

This reverts commit c5af258.

Author: beilunyang

package.json

@@ -34,8 +34,9 @@
     "drizzle-zod": "^0.7.0",
     "lucide-react": "^0.474.0",
     "nanoid": "^5.0.9",
-    "next": "15.2.4",
+    "next": "15.1.5",
     "next-auth": "5.0.0-beta.25",
+    "next-themes": "^0.4.4",
     "react": "^19.0.0",
     "react-dom": "^19.0.0",
     "react-hook-form": "^7.54.2",