v1.2.13 - Satellite data, dashboard, performance and documentation

1. Offline satellite data - 396 real satellites across all 13 groups
2. Satellite groups - fixed dead GROUP=other and empty iridium groups
3. Dashboard fixes - q quits, Tiangong displays correct data, and unused imports removed
4. Lazy-loaded images - Pillow and chafa no longer required at startup, with a new --no-image flag
5. Performance improvements - optimized observer calculations and parallel group fetching
6. Cache fixes - empty results no longer overwrite cached satellite data
7. Documentation - updated README with all modes, configuration, and flags
8. Man page - fixed documentation and removed duplicate man directory

Published - v1.2.13 is now available on GitHub and PyPI