perf: expand gateway capacity and prevent receipt replay

api/prisma/migrations/20260825143000_add_uplink_event_id/migration.sql

@@ -0,0 +1,3 @@
+ALTER TABLE "SmsUplinkMessage" ADD COLUMN "eventId" TEXT;
+
+CREATE UNIQUE INDEX "SmsUplinkMessage_eventId_key" ON "SmsUplinkMessage"("eventId");

api/prisma/schema.prisma

@@ -2117,6 +2117,7 @@ model SmsReceiptAnomaly {
 
 model SmsUplinkMessage {
   id              String   @id @default(cuid())
+  eventId         String?  @unique
   tenantId        String?
   applicationId   String?
   channelId       String