Upgrade and pin Vale to v3

[stevepiercy]

• Follow some of Vale's suggestions and fix errors and warnings.
• Add GitHub Workflow to build docs and run checks on links, spelling, grammar, and style.
• Closes Pin requirements #30.

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📚 Documentation preview 📚: https://plone-sphinx-theme--31.org.readthedocs.build/

[stevepiercy]

@davisagli I was today days old when I learned that pyproject.toml should list your packages, but not pins of packages, and let that stay in requirements-docs.txt.

This PR should handle the downstream issues that may arise from documentation. I also just realized that eventually any project that uses this theme could have a simplified requirements-docs.txt file that contains only plone-sphinx-theme==x.x.x.

Thanks for the nudge to pin packages. I never fully understood the benefits.

[davisagli]

@stevepiercy Btw, there are tools that can take a list of unpinned packages and generate a requirements.txt with the current latest pins.

I used to use pip-tools for this: https://hynek.me/til/pip-tools-and-pyproject-toml/

But now I would use uv, because it's faster and can correctly handle cases where the dependencies are resolved differently on different platforms. https://docs.astral.sh/uv/pip/compile/

[stevepiercy]

But now I would use uv, because it's faster and can correctly handle cases where the dependencies are resolved differently on different platforms. https://docs.astral.sh/uv/pip/compile/

Challenge accepted! I realize the deps could be better organized into 3 different buckets: install, develop, and release. Right now they're not well separated.

[stevepiercy]

Merging, and moving on to improving dep management with uv.