Format and lint all docs

[danbarr]

Summary

Format and lint all docs files per the new style guide.

This is not a full language/voice review, just the automated fixes, and simple items like normalizing title/heading sentence case.

Also resolves two lingering comments from #5320:

• Re-enable no-duplicate-heading markdownlint rule
• Fix order of operations in docs/README.md

Change Type

• Bug fix (resolves an issue without affecting existing features)
• Feature (adds new functionality without breaking changes)
• Breaking change (may impact existing functionalities or require documentation updates)
• Documentation (updates or additions to documentation)
• Refactoring or test improvements (no bug fixes or new functionality)

Testing

Ran all format/lint checks and confirmed site builds successfully.

Review Checklist:

• Reviewed my own code for quality and clarity.
• Added comments to complex or tricky code sections.
• Updated any affected documentation.
• Included tests that validate the fix or feature.
• Checked that related changes are merged.

[coveralls]

coverage: 56.635%. remained the same
when pulling 761d3e0 on danbarr:docs/format-all-docs
into a00a92f on mindersec:main.