Fix mkdocs build warnings (and assorted linting errors)

[day-jeff]

What are you trying to address

• Fix mkdocs build warnings "doc file contains an unrecognized relative link"
• While validating this PR, discovered Megalinter is throwing errors and warnings on a half dozen unrelated issues. I fixed all of 'em.

Checklist

[READY TO PR? Use the check-list below to ensure your branch is ready for PR.]

• [ ] Changes follow the repo structure and land in the appropriate folder and section
• [ ] No confidential information
• [ ] No duplicated content
• [ ] Labeled appropriately
• [ ] This PR was reviewed by at least one subject matter expert
• [ ] No lint check errors related to your changes

Note: You may see link check errors on pages you have not touched. This is normal, and due to either broken links or sites that reject link checker bots. The reviewer will help you get to a green state on these.

[github-actions[bot]]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ ACTION	actionlint	2		0	0.02s
✅ MARKDOWN	markdownlint	258		0	5.98s
✅ MARKDOWN	markdown-table-formatter	258		0	0.74s
✅ MDLINKCHECK	linkcheck	258		0	10.11s
✅ SPELL	cspell	269		0	11.56s
✅ YAML	prettier	10		0	1.47s
✅ YAML	yamllint	10		0	0.52s

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