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>

apps/api/src/modules/listings/domain/events/listing-price-changed.event.ts

@@ -0,0 +1,12 @@
+import type { DomainEvent } from '@modules/shared';
+
+export class ListingPriceChangedEvent implements DomainEvent {
+  readonly eventName = 'listing.price_changed';
+  readonly occurredAt = new Date();
+
+  constructor(
+    public readonly aggregateId: string,
+    public readonly oldPrice: bigint,
+    public readonly newPrice: bigint,
+  ) {}
+}