Periodically reconcile active overlay network state

[briceamen]

Problem

sand-agent restores active networks and endpoints at startup, while endpoint events update the ARP/FDB state when they are received. There is no periodic reconciliation if the stored state and the effective dataplane later diverge. Connectivity can therefore remain broken until sand-agent is restarted.

Relevant code:

• Networks are restored during agent startup
• ensureNetworks replays active endpoints
• Endpoint events apply ARP/FDB changes once

Expected behavior

sand-agent should periodically reconcile the effective state of active overlay networks and endpoints with the stored state, so connectivity can recover without restarting the agent.

The reconciliation should be idempotent and should not reactivate endpoints, republish endpoint events, or register duplicate network watchers.