docs-deps(deps): bump sphinx from 7.2.6 to 9.1.0 in /docs

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 7.2.6 to 9.1.0.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v7.2.6...v9.1.0)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-version: 9.1.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

docs/pyproject.toml

@@ -9,7 +9,7 @@ dependencies = [
     "linkify-it-py>=2.0.3",
     "matplotlib>=3.10.6",
     "myst-parser>=4.0.1",
-    "sphinx==7.2.6",
+    "sphinx==9.1.0",
     "sphinx-autobuild>=2025.8.25",
     "sphinx-copybutton>=0.5.2",
     "sphinx-design>=0.6.1",