feat: add dashboard with vehicle fleet overview (refs #2)

Implements responsive dashboard showing:
- Summary cards (vehicle count, upcoming maintenance, recent fuel logs)
- Vehicles needing attention with priority highlighting
- Quick action buttons for navigation
- Loading skeletons and empty states
- Mobile-first responsive layout (320px to 1920px+)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/features/dashboard/index.ts

@@ -0,0 +1,10 @@
+/**
+ * @ai-summary Dashboard feature public exports
+ */
+
+export { DashboardScreen } from './components/DashboardScreen';
+export { SummaryCards, SummaryCardsSkeleton } from './components/SummaryCards';
+export { VehicleAttention, VehicleAttentionSkeleton } from './components/VehicleAttention';
+export { QuickActions, QuickActionsSkeleton } from './components/QuickActions';
+export { useDashboardSummary, useVehiclesNeedingAttention } from './hooks/useDashboardData';
+export type { DashboardSummary, VehicleNeedingAttention, DashboardData } from './types';