feat: sshd watchdog for NetBird mesh node recovery #11
Description
Impact
When NetBird tunnel drops, node becomes unreachable until manual intervention.
Signal Source
Operational experience — nodes occasionally lose mesh connectivity.
Expected
Watchdog daemon detects NetBird disconnection, restarts service, alerts central meta-sentinel.
Blast Radius
Single node isolation; other nodes continue autonomously.
Rollback Plan
Disable watchdog cron; manual SSH reconnection as before.