fix(deps): update dependency next to v15

Author: renovate[bot]

package.json

@@ -23,7 +23,7 @@
     "@stackblitz/sdk": "^1.11.0",
     "@vercel/analytics": "^1.5.0",
     "@vercel/speed-insights": "^1.2.0",
-    "next": "^14.2.29",
+    "next": "^15.3.2",
     "nextra": "^2.13.4",
     "nextra-theme-docs": "^2.13.4",
     "react": "^18.3.1",