Initial implementation of fire show calculator ...

- Added gnexus-ui-kit as git submodule
- Created index.html with calculator UI
- Implemented formula solver for one unknown variable
- Added artist roster with role assignment
- Calculated royalties based on net amount after material costs
- Added localStorage persistence and JSON export/import
- Created docs/plan.md with project documentation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>