build(deps): bump next from 13.5.7 to 15.2.1

Bumps [next](https://github.com/vercel/next.js) from 13.5.7 to 15.2.1.
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](vercel/next.js@v13.5.7...v15.2.1)

---
updated-dependencies:
- dependency-name: next
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

docs/package.json

@@ -12,7 +12,7 @@
   "dependencies": {
     "@textea/json-viewer": "workspace:^",
     "gray-matter": "^4.0.3",
-    "next": "^13.5.7",
+    "next": "^15.2.1",
     "nextra": "2.13.3",
     "nextra-theme-docs": "2.13.3",
     "react": "^18.3.1",