feat: add unit tests for featured listings, neighborhood scores + price history chart

- Add unit tests for FeatureListingHandler (6 tests) and ActivateFeaturedListingHandler (6 tests)
- Add unit tests for NeighborhoodScoreServiceImpl (5 tests) and GetNeighborhoodScoreHandler (2 tests)
- Add PriceHistoryChart component with recharts LineChart for listing detail page
- Wire up price history API client and integrate chart into listing detail view

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/lib/listings-api.ts

@@ -132,6 +132,14 @@ export interface SearchListingsParams {
   limit?: number;
 }
 
+export interface PriceHistoryItem {
+  id: string;
+  oldPrice: string;
+  newPrice: string;
+  source: string;
+  changedAt: string;
+}
+
 export interface NeighborhoodScoreResult {
   district: string;
   city: string;
@@ -203,6 +211,9 @@ export const listingsApi = {
     return res.json() as Promise<{ mediaId: string; url: string }>;
   },
 
+  getPriceHistory: (listingId: string) =>
+    apiClient.get<PriceHistoryItem[]>(`/listings/${listingId}/price-history`),
+
   getNeighborhoodScore: (district: string, city: string = 'Hồ Chí Minh') =>
     apiClient.get<NeighborhoodScoreResult>(
       `/analytics/neighborhoods/${encodeURIComponent(district)}/score?city=${encodeURIComponent(city)}`,