Bump next in the npm_and_yarn group across 1 directory

Bumps the npm_and_yarn group with 1 update in the / directory: [next](https://github.com/vercel/next.js).

Updates `next` from 15.5.9 to 16.1.5
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](vercel/next.js@v15.5.9...v16.1.5)

Now Next.js has to receive the `--webpack` flag to silence the error

```
Next.js 16 Turbopack is enabled by default and custom webpack
configurations may need to be migrated to Turbopack.
```

At this time the migration to a Turbopack is complex because it doesn't
support the same level of loader chaining with plugin-based processors
that webpack does and our current webpack loader works by augmenting the
output of `@markdoc/next.js` which is the Next.js plugin that processes
the markdown files.

We'll look to migrate when Turbopack matures in this aspect.

---
updated-dependencies:
- dependency-name: next
  dependency-version: 16.1.5
  dependency-type: direct:production
  dependency-group: npm_and_yarn
...

Author: dependabot[bot]

package-lock.json

@@ -6,7 +6,7 @@
     "predev": "node scripts/fetch-image-sizes.mjs",
     "dev": "next dev",
     "prebuild": "node scripts/fetch-image-sizes.mjs",
-    "build": "next build",
+    "build": "next build --webpack",
     "start": "next start",
     "lint": "next lint",
     "prettier": "prettier --write '**/*.{ts,tsx,js,jsx,css,html}' --ignore-path .gitignore",
@@ -33,7 +33,7 @@
     "focus-visible": "^5.2.0",
     "framer-motion": "^10.16.1",
     "js-yaml": "^4.1.1",
-    "next": "^15.5.9",
+    "next": "^16.1.5",
     "next-themes": "^0.2.1",
     "postcss-focus-visible": "^6.0.4",
     "postcss-import": "^14.1.0",