chore: initial CLAUDE.md

Claude Code `/insights` proposed a number of suggestions.
These suggestions seem sensible as general guidance for the project

Assisted-by: Claude Opus 4.7

Author: david-allison

CLAUDE.md

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+## Refactoring Scope
+- Constrain scope tightly: do not modify unrelated files, themes, or settings 'while you're in there'.
+
+## Verification
+- For bug fixes, write the failing regression test FIRST and confirm it fails before applying the fix.