chore(deps): bump shibuya from 2025.8.16 to 2025.10.20 in /docs

Bumps [shibuya](https://github.com/lepture/shibuya) from 2025.8.16 to 2025.10.20.
- [Release notes](https://github.com/lepture/shibuya/releases)
- [Changelog](https://github.com/lepture/shibuya/blob/main/docs/changelog.rst)
- [Commits](lepture/shibuya@2025.8.16...2025.10.20)

---
updated-dependencies:
- dependency-name: shibuya
  dependency-version: 2025.10.20
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

docs/requirements.txt

@@ -1,4 +1,4 @@
-shibuya==2025.8.16
+shibuya==2025.10.20
 sphinx==7.4.7
 sphinx-click==6.0.0
 myst_parser==4.0.1