Add explicit mode switcher: Sum vs Payouts ...

- 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>

Split royalties equally among people with the same role ...

- Rop, Rot, Rok are now divided by the number of people assigned to each role
- Updated calculation docs to reflect the split behavior
- Rom remains a fixed team budget expense (not assigned to people)

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

Add calculation docs and redesign UI with better components ...

- Added docs/calculations.md explaining formula, Base, royalties, auto-calc
- Redesigned UI using Cards, Metric Cards, Alerts, Badges, Page Header
- Fixed icon buttons using `with-icon` class
- Replaced description-list summary with metric cards grid
- Added accent styling for total S metric card
- Updated message display to use alert components
- Fixed duplicate export button IDs

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