Add job status endpoint, persist lastJobId; replace in-process queue with BullMQ-based queue and worker; link job status in UI

prisma/schema.prisma

@@ -15,6 +15,7 @@ model Stock {
   lastDecision     String?
   lastExplanation  String?
   lastExecutionPlan String?
+  lastJobId        String?
   createdAt        DateTime @default(now())
   updatedAt        DateTime @updatedAt
 }