Zircd – Version 0.51 released

**FIX**: Link self-healing and state reconciliation:

Triggered by a 7-day silent outage, CIABBS/SpaghettiHut link to the main server died on 2026-05-31 and was never re-established until a manual restart of both main and hub1 on 2026-06-07.

**NEW**: Layer 1 – robust half-open detection on the initiator.

**NEW**: Layer 2 – mesh-assisted reconnect nudge.

**NEW**: Layer 3 – passive-side down-link alerting.

**NEW**: Feature 2 – periodic full re-sync.

**FIX**: remote JOIN – phantom re-join spam from re-sync.

**Hardening**: `PingTimeout` now has a defaults-dict entry (“180”) and a `fallback=180` on its config read, matching PingInterval/ResyncInterval. A zircd.cfg missing PingTimeout no longer crashes startup with NoOptionError.