Migrate task queue from in-memory to BullMQ + Redis

Replace the volatile in-memory Map/Set queue with BullMQ backed by Redis
for persistence across restarts, automatic retry with exponential backoff,
and non-blocking workspace cleanup.

- Two queues: workspace-create (concurrency-limited) and workspace-cleanup
  (with polling instead of sleep-based stop→delete)
- Active workspaces tracked in Redis hash for dedup across restarts
- Stale sweep every 10 minutes catches orphaned workspaces
- Graceful shutdown on SIGTERM/SIGINT
- Replace node-cron with BullMQ repeatable jobs

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

k8s/redis.yaml

@@ -0,0 +1,69 @@
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: redis-data
+  namespace: sdlc-orchestrator
+spec:
+  accessModes:
+    - ReadWriteOnce
+  resources:
+    requests:
+      storage: 1Gi
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: redis
+  namespace: sdlc-orchestrator
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: redis
+  template:
+    metadata:
+      labels:
+        app: redis
+    spec:
+      containers:
+        - name: redis
+          image: redis:7-alpine
+          args: ["--appendonly", "yes"]
+          ports:
+            - containerPort: 6379
+          volumeMounts:
+            - name: data
+              mountPath: /data
+          resources:
+            requests:
+              cpu: 50m
+              memory: 64Mi
+            limits:
+              cpu: 200m
+              memory: 256Mi
+          livenessProbe:
+            exec:
+              command: ["redis-cli", "ping"]
+            initialDelaySeconds: 5
+            periodSeconds: 30
+          readinessProbe:
+            exec:
+              command: ["redis-cli", "ping"]
+            initialDelaySeconds: 3
+            periodSeconds: 10
+      volumes:
+        - name: data
+          persistentVolumeClaim:
+            claimName: redis-data
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: redis
+  namespace: sdlc-orchestrator
+spec:
+  selector:
+    app: redis
+  ports:
+    - port: 6379
+      targetPort: 6379