Add comprehensive documentation for the command zone feature.
Developer documentation:
- command_zone_architecture.md: detailed architecture overview
- Layer separation (types, state, logic, graphics)
- Component interactions and dependencies
- Testing strategy and coverage
- Index update to include new architecture doc
User documentation:
- commander_format.md: how to use Commander format in Cockatrice
- Zone configuration options
- Gameplay mechanics (commander tax, zone reveals)
- Tips for Commander games
- Index update to include new format doc
