Bump next from 15.3.3 to 15.4.8 in /src/frontend

Bumps [next](https://github.com/vercel/next.js) from 15.3.3 to 15.4.8.
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](vercel/next.js@v15.3.3...v15.4.8)

---
updated-dependencies:
- dependency-name: next
  dependency-version: 15.4.8
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

src/frontend/apps/conversations/package.json

@@ -39,7 +39,7 @@
     "lottie-react": "^2.4.1",
     "luxon": "3.6.1",
     "micromark-extension-llm-math": "3.1.1-20250610",
-    "next": "15.3.3",
+    "next": "15.4.8",
     "posthog-js": "1.249.3",
     "react": "*",
     "react-aria-components": "1.9.0",