npm: bump vitepress from 1.6.3 to 1.6.4

Bumps [vitepress](https://github.com/vuejs/vitepress) from 1.6.3 to 1.6.4.
- [Release notes](https://github.com/vuejs/vitepress/releases)
- [Changelog](https://github.com/vuejs/vitepress/blob/v1.6.4/CHANGELOG.md)
- [Commits](vuejs/vitepress@v1.6.3...v1.6.4)

---
updated-dependencies:
- dependency-name: vitepress
  dependency-version: 1.6.4
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

package-lock.json

@@ -21,6 +21,6 @@
     "eslint-plugin-prettier": "^5.5.4",
     "prettier": "^3.6.2",
     "sass": "^1.90.0",
-    "vitepress": "^1.6.3"
+    "vitepress": "^1.6.4"
   }
 }