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/hooks/useListingDetail.ts

@@ -0,0 +1,42 @@
+import { useState, useRef, useCallback } from 'react';
+import type { AuthUser } from '@/auth/types';
+import type { ListingDetailData } from '@/types';
+import { fetchListingDetail } from '@/services';
+
+export function useListingDetail(user: AuthUser | null) {
+  const [detail, setDetail] = useState<ListingDetailData | null>(null);
+  const [isLoading, setIsLoading] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+  const cache = useRef<Map<string, ListingDetailData>>(new Map());
+
+  const loadDetail = useCallback(
+    async (listingId: number, listingType: 'RENT' | 'BUY' = 'RENT') => {
+      if (!user) return;
+      const cacheKey = `${listingId}-${listingType}`;
+      const cached = cache.current.get(cacheKey);
+      if (cached) {
+        setDetail(cached);
+        return;
+      }
+      setIsLoading(true);
+      setError(null);
+      try {
+        const data = await fetchListingDetail(user, listingId, listingType);
+        cache.current.set(cacheKey, data);
+        setDetail(data);
+      } catch (e) {
+        setError(e instanceof Error ? e.message : String(e));
+      } finally {
+        setIsLoading(false);
+      }
+    },
+    [user],
+  );
+
+  const clearDetail = useCallback(() => {
+    setDetail(null);
+    setError(null);
+  }, []);
+
+  return { detail, isLoading, error, loadDetail, clearDetail };
+}