Add GitLab formatting rules and code review guidelines to CLAUDE.md

- Add GitLab Formatting Rules section (avoid accidental issue links with #N)
- Add Code Review Guidelines with:
  - Publishing reviews workflow (threads + summary)
  - Naming conventions (private attributes, exceptions)
  - General coding practices (super().__init__, docstrings, error handling)
  - Class structure ordering guidelines
  - Test conventions (AAA format, standalone functions)
  - Code quality (avoid suppressions)

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>