Implement the Dashboard screen (Issue #30) as the new start destination:
- DashboardUiState: data class with sections for category summaries,
total value, supply range, expiry warnings, and min stock warnings
- DashboardViewModel: combines Item/Category flows with all five
Use Cases from #29 (CalculateCategorySummary, CalculateTotalValue,
CalculateSupplyRange, GetExpiryWarnings, GetMinStockWarnings)
- DashboardScreen: Material 3 layout with color-coded cards for
summary overview, supply range (days), expiry warnings (red/orange),
and min stock warnings (red), plus per-category cards
- Navigation: Dashboard added as startDestination, ItemListScreen
gets a Dashboard menu entry for back-navigation
- 9 unit tests covering empty state, category summaries, total value,
supply range, expiry/min-stock warnings, and reactive updates
Closes#30
b12684e6fc