Add tappable cards, detail bottom sheet, swipe gestures, and favorites view

- Decision types, services (decisionService, listingDetailService), and index exports
- useDecisions hook with optimistic updates and Map-based state
- useListingDetail hook with session-level caching
- PhotoCarousel component using embla-carousel-react
- ListingDetail component with full property info, like/dislike buttons
- ListingDetailSheet using vaul Drawer (slide-up bottom sheet)
- SwipeablePropertyCard with @use-gesture/react and @react-spring/web
- SwipeReviewMode for mobile full-screen swipe review
- FavoritesView with virtualized liked listings and remove button
- App.tsx integration: decision state, client-side disliked filtering, detail sheet, swipe handlers
- ListView conditionally renders SwipeablePropertyCard when handlers provided
- StatsBar adds 'saved' view mode with heart icon
- Header adds liked count indicator
- New deps: vaul, embla-carousel-react, @use-gesture/react, @react-spring/web

frontend/src/services/index.ts

@@ -6,3 +6,4 @@ export { fetchTasksForUser, fetchTaskStatus, cancelTask, clearAllTasks, type Can
 export { checkBackendHealth, type HealthStatus, type HealthCheckResult } from './healthService';
 export { fetchUserPOIs, createPOI, updatePOI, deletePOI, triggerPOICalculation, fetchPOIDistances } from './poiService';
 export { fetchDecisions, setDecision, clearDecision } from './decisionService';
+export { fetchListingDetail } from './listingDetailService';