fix: package.json & package-lock.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-NEXT-10176058

Author: snyk-bot

package-lock.json

@@ -56,7 +56,7 @@
     "locomotive-scroll": "^4.1.4",
     "markmap-lib": "^0.17.2",
     "markmap-view": "^0.17.2",
-    "next": "^15.0.3",
+    "next": "^15.1.6",
     "openai": "^4.71.1",
     "react": "^18.3.1",
     "react-dom": "^18.3.1",