## Changes
- Remove `activeSessions` parameter from health check (was never populated)
- Add gateway session lookup via `openclaw gateway call status`
- Add issue label lookup via `provider.getIssue(issueId)`
- Implement detection matrix with 6 issue types:
- session_dead: active worker but session missing in gateway
- label_mismatch: active worker but issue not in Doing/Testing
- stale_worker: active for >2h
- stuck_label: inactive but issue has Doing/Testing label
- orphan_issue_id: inactive but issueId set
- issue_gone: active but issue deleted/closed
## Files
- lib/services/health.ts — complete rewrite with three-source triangulation
- lib/tools/health.ts — remove activeSessions param, fetch sessions from gateway
- lib/services/heartbeat.ts — remove empty activeSessions calls, pass sessions map
825c5e6f50