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/migrations/20260416200000_add_price_history/migration.sql

@@ -0,0 +1,16 @@
+-- CreateTable: PriceHistory (listing price change tracking)
+CREATE TABLE "PriceHistory" (
+    "id" TEXT NOT NULL,
+    "listingId" TEXT NOT NULL,
+    "oldPrice" BIGINT NOT NULL,
+    "newPrice" BIGINT NOT NULL,
+    "changedAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "PriceHistory_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE INDEX "PriceHistory_listingId_changedAt_idx" ON "PriceHistory"("listingId", "changedAt" DESC);
+
+-- AddForeignKey
+ALTER TABLE "PriceHistory" ADD CONSTRAINT "PriceHistory_listingId_fkey" FOREIGN KEY ("listingId") REFERENCES "Listing"("id") ON DELETE CASCADE ON UPDATE CASCADE;