Prune DESIGN.md and CLAUDE.md guidance

Drop the "Don't" list and the "Rule" suffixes from DESIGN.md, retitle the
named rules as things to keep consistent, and move the general-rules note
there from CLAUDE.md.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
4f26c81b43Dara Adedeji committed on 9/12/2026, 3:21:58 AMparent34f3c78

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