Phase 5: Outbox DLQ, Monitoring, Consumer-Registry

- Migration 0092: DLQ columns (error_message, failed_at) + consumer_inbox RLS fix
- outbox.py: DLQ logic, replay functions, stats, consumer registry
- app/routes/outbox.py: 5 API endpoints (stats, failed, replay, replay-all, consumer-registry)
- outbox_deliveries tracking per consumer handler
- 18/18 tests passing

app/models/consumer_inbox.py

@@ -25,7 +25,7 @@ class ConsumerInbox(Base):
     )
 
     id: Mapped[uuid.UUID] = mapped_column(
-        PGUUID(as_uuid=True), primary_key=True, default=uuid.uuid4
+        PGUUID(as_uuid=True), primary_key=True, server_default=func.gen_random_uuid(),
     )
     event_id: Mapped[uuid.UUID] = mapped_column(
         PGUUID(as_uuid=True),