Add dark mode styling to docs

[Brett-Best]

Summary

• add dark-mode styling to the Jazzy-generated documentation
• cover page chrome, tables, inline/code blocks, search/typeahead, blockquotes, asides, and syntax highlighting
• use APCA-audited Tailwind palette values so checked text pairs clear Lc 60

Validation

• ruby -e 'require "yaml"; YAML.load_file(".jazzy.yaml")'
• git diff --check
• APCA audit script: 28 checked pairs >= Lc 60
• swift run swiftlint generate-docs
• bundle exec jazzy --build-tool-arguments=--disable-sandbox

[SimplyDanny]

I wonder if this can go into a separate file for easier access, syntax highlighting, ... Did you try that or check for an option?