Update dependency fumadocs-mdx to v15

Author: renovate[bot]

package.json

@@ -17,7 +17,7 @@
     "clsx": "^2.1.1",
     "framer-motion": "^12.23.24",
     "fumadocs-core": "^16.0.1",
-    "fumadocs-mdx": "^13.0.0",
+    "fumadocs-mdx": "^15.0.0",
     "fumadocs-ui": "^16.0.1",
     "lucide-react": "^0.546.0",
     "next": "^16.0.0",