fix(nostr-client): restore subscriptions and availability on relay reconnect

When a relay reconnects after a disconnect, all active subscriptions
(including Lightning.Pub RPC listener) are now re-established on the
new relay instance. Previously subscriptions were lost permanently.

Also publishes availability broadcast immediately on reconnect instead
of waiting up to 5 minutes for the next heartbeat.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/machine/src/composables/useAvailabilityBroadcast.ts

@@ -116,6 +116,12 @@ export function useAvailabilityBroadcast(options: UseAvailabilityBroadcastOption
   // Publish immediately on setup
   publish(computeSnapshot())
 
+  // Re-publish immediately when relay reconnects (don't wait for next heartbeat)
+  nostrClient.on('connect', () => {
+    console.log('[Availability] Relay reconnected, publishing immediately')
+    publish(computeSnapshot())
+  })
+
   function stop() {
     clearInterval(heartbeatInterval)
   }