feat(api): add price history, Stringee SMS, Zalo OA, WebSocket notifications, and feature-listing command

- Add PriceHistory model + migration, price-changed domain event, and event handler
- Add GetPriceHistory query handler and controller endpoint
- Implement StringeeSmsService and ZaloOaService with unit tests
- Add Zalo ZNS templates for Vietnamese notification messages
- Add WebSocket notification gateway for real-time push
- Add FeatureListingCommand for promoted listings
- Apply remaining consistent-type-imports lint fixes across API modules

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

prisma/schema.prisma

@@ -333,9 +333,10 @@ model Listing {
   createdAt        DateTime        @default(now())
   updatedAt        DateTime        @updatedAt
 
-  transactions Transaction[]
-  inquiries    Inquiry[]
-  orders       Order[]
+  transactions  Transaction[]
+  inquiries     Inquiry[]
+  orders        Order[]
+  priceHistories PriceHistory[]
 
   // --- Single-column indexes ---
   @@index([status])
@@ -357,6 +358,17 @@ model Listing {
   @@index([status, transactionType, priceVND])
 }
 
+model PriceHistory {
+  id        String   @id @default(cuid())
+  listingId String
+  listing   Listing  @relation(fields: [listingId], references: [id], onDelete: Cascade)
+  oldPrice  BigInt
+  newPrice  BigInt
+  changedAt DateTime @default(now())
+
+  @@index([listingId, changedAt(sort: Desc)])
+}
+
 // =============================================================================
 // SEARCH
 // =============================================================================