chore: bump Next.js to v15.5.9 and update lockfile

Author: mittalyashu

package.json

@@ -22,7 +22,7 @@
     "fumadocs-typescript": "^4.0.4",
     "fumadocs-ui": "^15.7.11",
     "lucide-react": "^0.552.0",
-    "next": "15.5.6",
+    "next": "15.5.9",
     "prettier": "^3.6.2",
     "react": "19.2.0",
     "react-dom": "19.2.0",