fix(nostr): close SimplePool after publishing to prevent connection leak

Each sendEvent() call created a new SimplePool() but never closed it,
causing relay WebSocket connections to accumulate indefinitely (~20/min).

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[]) {