feat(service): P4 doc-faithfulness — SLA placeholder columns, issueSubclass, traceId on state.changed

Adds ticket.slaDueAt + ticket.issueSubclass + queue.slaPolicyRef (placeholder
columns, no timer logic until P7) and propagates ticket.traceId onto
ticket.state.changed events (assignment + transition). 45 tests still green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/iios-service/prisma/schema.prisma

@@ -414,6 +414,7 @@ model IiosSupportQueue {
   scope            IiosScope @relation(fields: [scopeId], references: [id], onDelete: Cascade)
   name             String
   supportTier      String    @default("REGULAR")
+  slaPolicyRef     String? // SLA placeholder (no timer logic until P7)
   assignmentPolicy Json?
   enabled          Boolean   @default(true)
   createdAt        DateTime  @default(now())
@@ -454,6 +455,8 @@ model IiosTicket {
   state                   IiosTicketState    @default(NEW)
   priority                IiosTicketPriority @default(P3)
   issueClass              String?
+  issueSubclass           String?
+  slaDueAt                DateTime? // SLA placeholder (no timer logic until P7)
   createdFromInteractionId String?
   createdFromInteraction  IiosInteraction?   @relation(fields: [createdFromInteractionId], references: [id])
   traceId                 String?