Pin jupyter-book<2 to fix docs build in CI

jupyter-book v2 uses a new MyST config format (myst.yml) and no longer
supports the legacy _config.yml/_toc.yml used by this project, causing
the build to produce no output.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: PavelMakarchuk

changelog.d/fix-docs-build.fixed.md

@@ -0,0 +1 @@
+Pin jupyter-book to v1 to fix documentation build in CI.

pyproject.toml

@@ -41,7 +41,7 @@ dependencies = [
 dev = [
     "build",
     "furo",
-    "jupyter-book",
+    "jupyter-book<2",
     "markupsafe",
     "pydata-sphinx-theme",
     "sphinx",