feat(extensions): pay from caller's balance via PayAppUserInvoice

When userPubkey is provided, resolve the ApplicationUser and call
applicationManager.PayAppUserInvoice instead of paymentManager.PayInvoice
directly. This ensures notifyAppUserPayment fires, sending
LiveUserOperation events via Nostr for real-time balance updates.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/services/nostr/nostrPool.ts

@@ -205,6 +205,7 @@ export class NostrPool {
         const log = getLogger({ appName: keys.name })
         this.log(`📤 Publishing Kind ${event.kind} event to ${relays.length} relay(s): ${relays.join(', ')}`)
         const pool = new SimplePool()
+        try {
             await Promise.all(pool.publish(relays, signed).map(async p => {
                 try {
                     await p
@@ -220,6 +221,9 @@ export class NostrPool {
             } else {
                 this.log(`✅ Kind ${event.kind} event published successfully (id: ${signed.id.slice(0, 16)}...)`)
             }
+        } finally {
+            pool.close(relays)
+        }
     }
 
     private getRelays(initiator: SendInitiator, requestRelays?: string[]) {