fix(machine): guard the availability beacon sign against bunker blips

The beacon's createSignedEvent (a bunker round-trip) sat OUTSIDE its try/catch,
and publish() is fire-and-forget — so a transient BunkerTimeoutError /
BunkerRejectedError during the periodic sign surfaced as an uncaught promise
rejection (seen on the Sintra after a bunker watchdog blip during the cash-in
smoke). Move the sign inside the try; the beacon re-publishes every interval, so
swallow + log is correct.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/machine/src/composables/useAvailabilityBroadcast.ts

@@ -73,19 +73,22 @@ export function useAvailabilityBroadcast(options: UseAvailabilityBroadcastOption
       model,
     })
 
+    // Signing goes through the bunker, so it can throw BunkerTimeoutError /
+    // BunkerRejectedError — keep it INSIDE the try so a transient signer blip
+    // is swallowed (the beacon re-publishes every interval) rather than
+    // surfacing as an uncaught rejection. `publish()` is fire-and-forget.
+    try {
       const event = await createSignedEvent(signer, {
         kind: 30078,
         created_at: Math.floor(Date.now() / 1000),
         tags: [['d', 'atm-availability']],
         content,
       })
-
-    try {
       await nostrClient.publish(event)
       lastSnapshot = snap
       console.log('[Availability] Published:', content)
     } catch (e) {
-      console.warn('[Availability] Failed to publish:', e)
+      console.warn('[Availability] Publish failed (sign or relay):', e)
     }
   }