Relay health monitor (latency, reconnect tracking)

[ermeme]

Milestone: 3 — Protocol gaps
Type: protocol / ux
Priority: low

Today the only relay status comes from the SDK. v1 has lib/features/relays/relay_health_monitor.dart that tracks latency, reconnect count, last error, and time-since-connect per relay.

Scope

• Per-relay health record in Rust: state, last RTT, reconnect attempts, last error, last successful read.
• Expose via the bridge.
• Show the data in the Relays settings card (replace the binary on/off dot with a colored health indicator + tooltip).