chore: initial CLAUDE.md

[david-allison]

Note

Assisted-by: Claude Opus 4.7

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

Checklist

• You have a descriptive commit message with a short title (first line, max 50 chars).
• You have commented your code, particularly in hard-to-understand areas
• You have performed a self-review of your own code
• UI changes: include screenshots of all affected screens (in particular showing any new or changed strings)
• UI Changes: You have tested your change using the Google Accessibility Scanner