Add a centralized color module (cli/src/color.rs) that respects the
NO_COLOR environment variable per https://no-color.org/
Changes:
- Add color.rs module with helper functions for colored output
- Refactor all hardcoded ANSI escape codes to use the color module
- Add tests for color formatting functions
- Update AGENTS.md with color module usage guidelines
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
