build(deps): bump storybook from 8.6.14 to 8.6.15 in /docs-ui

Bumps [storybook](https://github.com/storybookjs/storybook/tree/HEAD/code/core) from 8.6.14 to 8.6.15.
- [Release notes](https://github.com/storybookjs/storybook/releases)
- [Changelog](https://github.com/storybookjs/storybook/blob/next/CHANGELOG.md)
- [Commits](https://github.com/storybookjs/storybook/commits/v8.6.15/code/core)

---
updated-dependencies:
- dependency-name: storybook
  dependency-version: 8.6.15
  dependency-type: direct:production
...

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

docs-ui/package.json

@@ -38,7 +38,7 @@
     "react": "19.1.1",
     "react-dom": "19.1.1",
     "shiki": "^3.13.0",
-    "storybook": "^8.6.12"
+    "storybook": "^8.6.15"
   },
   "devDependencies": {
     "@octokit/rest": "^22.0.1",