sec: bump next 15.5.14 → 15.5.15

Upgrades Next.js to resolve a HIGH severity vulnerability flagged by
Snyk against agentex-ui. Lockfile regenerated via `npm install` (next
and all @next/swc-* native binaries updated in place).

Author: scale-ballen

agentex-ui/package-lock.json

@@ -39,7 +39,7 @@
     "date-fns": "^4.1.0",
     "framer-motion": "^12.23.24",
     "lucide-react": "^0.525.0",
-    "next": "15.5.14",
+    "next": "15.5.15",
     "next-themes": "^0.4.6",
     "react": "^19.1.1",
     "react-dom": "^19.1.1",