Bump the production-dependencies group across 1 directory with 3 updates

Bumps the production-dependencies group with 3 updates in the /docs directory: [next](https://github.com/vercel/next.js), [nextra](https://github.com/shuding/nextra) and [nextra-theme-docs](https://github.com/shuding/nextra).


Updates `next` from 15.1.4 to 15.1.6
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](vercel/next.js@v15.1.4...v15.1.6)

Updates `nextra` from 3.3.1 to 4.1.0
- [Release notes](https://github.com/shuding/nextra/releases)
- [Commits](https://github.com/shuding/nextra/compare/[email protected]@4.1.0)

Updates `nextra-theme-docs` from 3.3.1 to 4.1.0
- [Release notes](https://github.com/shuding/nextra/releases)
- [Commits](https://github.com/shuding/nextra/compare/[email protected]@4.1.0)

---
updated-dependencies:
- dependency-name: next
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: production-dependencies
- dependency-name: nextra
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: production-dependencies
- dependency-name: nextra-theme-docs
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: production-dependencies
...

Signed-off-by: dependabot[bot] <[email protected]>

docs/package.json

@@ -1,8 +1,8 @@
 {
 	"dependencies": {
-		"next": "15.1.4",
-		"nextra": "^3.3.1",
-		"nextra-theme-docs": "^3.3.1",
+		"next": "15.1.6",
+		"nextra": "^4.1.0",
+		"nextra-theme-docs": "^4.1.0",
 		"react": "^19.0.0",
 		"react-dom": "^19.0.0",
 		"source-map-support": "^0.5.21"