Teach Duo code review to catch (and not suggest) html->text fallback

What does this MR do and why?

Duo suggests things it really shouldn't:

Teach it:

1. not to;
2. what to suggest instead;
3. when nothing needs suggesting at all; and,
4. to catch these when introduced in the MR.

Also rerun the AI principles distiller since my local push was failing without it. This normally gets reconciled daily AFAICT, but needs to be done manually if there's been any drift and you want to make changes to the review instructions that aren't distilled in yet.

See https://docs.gitlab.com/development/documentation/ai-instruction-files-documentation/#automated-review-file for more information about this file.

References

• https://gitlab.com/gitlab-org/gitlab/-/work_items/591065+
• https://gitlab.com/gitlab-org/gitlab/-/work_items/591863+
• https://gitlab.com/gitlab-org/gitlab/-/work_items/593051+
• html||text is an antipattern and must be elimin... (#605415 - closed)
• !231205 (comment 3534994633)

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