Downgrade Next.js from v15.5.9 to v13.5.6 to fix dependency conflict

Co-authored-by: AzadZedan <172204218+AzadZedan@users.noreply.github.com>

Author: Copilot

package.json

@@ -28,7 +28,7 @@
     "interweave": "^13.1.0",
     "meilisearch": "^0.32.3",
     "nanostores": "^0.7.4",
-    "next": "^15.5.9",
+    "next": "^13.5.6",
     "next-contentlayer": "^0.3.4",
     "next-seo": "^5.15.0",
     "next-themes": "^0.2.1",