Pin zensical version

[stuitje]

Pin Zensical version to the older version of 0.0.39 (newest release: 0.0.41) to hopefully fix the problem with the documentation build.

I also added a dark-mode version of the PROTEUS schematic (this schematic might be switched later; but for now this might be a nice addition).

[Copilot]

Pull request overview

This PR aims to stabilize the documentation build by pinning the zensical documentation tool to a known-working version, and improves docs presentation by switching the PROTEUS schematic to local light/dark-mode assets.

Changes:

• Pin zensical to 0.0.39 in the docs optional dependency set to avoid regressions impacting the docs build.
• Replace externally hosted PROTEUS schematic image links with locally versioned light/dark-mode images in documentation pages.
• Add a dark-mode schematic variant (and reference both variants using #only-light / #only-dark fragments).

Reviewed changes

Copilot reviewed 3 out of 5 changed files in this pull request and generated no comments.

File	Description
pyproject.toml	Pins zensical in the docs extra to stabilize docs builds.
docs/proteus_framework.md	Updates schematic embedding to use local light/dark assets.
docs/Explanations/proteus.md	Updates schematic embedding to use local light/dark assets with correct relative paths.

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[nichollsh]

Docs build successfully on my laptop with zensical==0.0.39 and python==3.12.12. Dark/light switch mode schematic works and looks great.