fix: remove legacy Jupyter Book config and clean stale nav refs

[joamatab]

Summary

• Delete legacy _toc.yml and _config.yml (docs now use zensical)
• Remove zensical.toml nav entries pointing to deleted stub files
• Remove mkdocs-pdf.yml nav entries pointing to deleted stub files

Test plan

• Verify docs build succeeds

Summary by Sourcery

Build:

• Delete obsolete docs/_config.yml and docs/_toc.yml Jupyter Book configuration files.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

This PR removes legacy Jupyter Book configuration files now superseded by zensical-based docs configuration, and is expected to be accompanied by cleanup of stale navigation references in zensical and mkdocs configs.

File-Level Changes

Change	Details	Files
Remove obsolete Jupyter Book configuration now that docs are managed by zensical	Delete legacy Jupyter Book site configuration file Delete legacy Jupyter Book table-of-contents configuration file	docs/_config.yml docs/_toc.yml

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[gemini-code-assist]

Code Review

This pull request removes the Jupyter Book configuration and table of contents files, signaling a transition to a new documentation system. Feedback focuses on ensuring a complete migration: the README should be updated to reflect the change, and critical settings—such as type aliases, API documentation layouts, and CI safety checks—need to be ported over. Additionally, the reviewer noted that several core pages and demo sections currently lack counterparts in the new navigation structure, which could lead to inaccessible content.

I am having trouble creating individual review comments. Click here to see my feedback.

docs/_config.yml (1)

The removal of the Jupyter Book configuration is consistent with the transition to zensical/mkdocs. However, the README.md (line 107) still describes the docs/ directory as "Jupyter Book documentation (Sphinx)". This description should be updated to reflect the new documentation system to maintain accuracy for contributors.

docs/_config.yml (49-75)

Several important documentation settings are being removed without apparent counterparts in the new configuration. Specifically, autodoc_type_aliases (lines 52-74) are essential for readable type hints, autodoc_typehints: description (line 49) controls the layout of API docs, and nb_execution_raise_on_error: true (line 75) is a critical CI safety check. These should be migrated to the mkdocstrings and notebook execution settings in the new system to maintain documentation quality and build reliability.

docs/_toc.yml (8-23)

The removal of these navigation entries makes several core pages (tech, cells_fixed, cells2_reference), the entire "Demos" section, and external links (gplugins, gdsfactory) inaccessible. If these are not actually stale stubs, they should be migrated to the new navigation configuration. Note that the execution exclusion for palace_demo_cpw (previously in _config.yml line 14) also needs to be carried over to the new system to prevent potential build issues.