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/secret.yaml.example

@@ -15,8 +15,11 @@ stringData:
   GITEA_DEV_TOKEN: "<gitea-claude-dev-token>"
   GITEA_REVIEW_TOKEN: "<gitea-claude-review-token>"
   ANTHROPIC_API_KEY: "<anthropic-api-key>"
+  CLAUDE_OAUTH_TOKEN: "<claude-code-max-oauth-token>"
   GITEA_URL: "https://gitea.samson.media"
   BOT_DEV_USERNAME: "claude-dev"
   BOT_REVIEW_USERNAME: "claude-review"
+  CALLBACK_URL: "https://sdlc.samson.media"
+  REDIS_URL: "redis://redis.sdlc-orchestrator.svc.cluster.local:6379"
   # Comma-separated: org/repo=clone_url
   MAINTENANCE_REPOS: "claude/babble=https://gitea.samson.media/claude/babble.git"