v3.1.0: Heartbeat/Lease/Recovery Integration

New Features

• Full heartbeat/lease/recovery integration into cluster service
• NodeManager, LeaseManager, Watchdog, Recovery wired into app
• Lease-based task scheduling and automatic recovery
• E2E tested on multi-machine Proxmox LXC environment

Bug Fixes

• Fixed HeartbeatRequest missing load field
• Fixed _on_watchdog_event triggering NodeEvent for Recovery
• Fixed RevokeAllForNode() handling both active and expired leases
• Fixed tasks_mod.init receiving lease_manager

Testing

• 31 new E2E tests (heartbeat lifecycle, lease lifecycle, failure recovery, integration, edge cases)
• 170+ total tests pass