- Added chip-group toggle between 'Сумма' and 'Выплаты' modes
- In Sum mode: S is readonly/computed, Z is manual input
- In Payout mode: Z is readonly/computed, S is manual input
- Removed confusing auto-calculation logic for single missing field
- Mode persists in localStorage and export/import
- Updated docs with clear explanation of both modes
- Added input-readonly styling for disabled fields

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