Add dark-mode docs styling and colorized CLI reference output

[t-kalinowski]

Summary

• Update the docs site to support light and dark themes, with a dedicated dark stylesheet so the reference pages remain readable in both modes.
• Render the live ir help output as colored HTML instead of plain text, so the documentation mirrors the real CLI output more closely and is easier to scan.
• Build the current ir binary during docs publishing and expose it to Quarto, instead of downloading a released artifact, so the reference page always reflects the checked-out source.
• Keep the CLI help color-aware in the app itself by enabling clap's automatic color handling.
• Add regression coverage for the docs pages to verify dark-mode styling, colored help rendering, and the build-time wiring used by the reference page.