* refactor: reorganize mdbook config and contributing docs
* fix: correct preprocessor relative paths in book.toml configs
The preprocessor command paths had one extra ../ level, resolving
outside the repo root. Fix from ../../../../tools/ to ../../../tools/.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>