contributing: tighten AI usage policy (#18388)
* contributing: tighten AI usage policy
* refactor AGENTS.md
* proofreading
* update contributing
* add claude.md
* add trailing newline
* add note about dishonest practices
* rm point about dishonest
* rm requirement watermarking
* add .gemini/settings.json
* allow initially AI-generated content
* revise
* Update CONTRIBUTING.md
Co-authored-by: Johannes Gäßler <johannesg@5d6.de>
* improve
* trailing space
* Apply suggestions from code review
Co-authored-by: Johannes Gäßler <johannesg@5d6.de>
* update
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Co-authored-by: Johannes Gäßler <johannesg@5d6.de>
