fix: periodic keep-alive to revive relays in long backoff

When a relay enters a long backoff (5 min, e.g. host unreachable or
a server returned an HTTP error during handshake), the per-relay
delayToConnectInSeconds blocks reconnect attempts for up to 5 minutes.
Without a wakeup, nothing inside NostrClient revisits that relay until
the next subscribe/count/publish.

Add a keep-alive coroutine that calls reconnectIfNeedsTo(false) every
60s while the client is active. The per-relay backoff still gates the
actual reconnect, so dead relays are not hammered, but a relay whose
backoff window has elapsed is reconnected within ~60s of becoming
eligible.

The job lives in scope and is cancelled by close().

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip01Core/relay/client/NostrClient.kt

@@ -42,6 +42,7 @@ import kotlinx.coroutines.FlowPreview
 import kotlinx.coroutines.IO
 import kotlinx.coroutines.SupervisorJob
 import kotlinx.coroutines.cancel
+import kotlinx.coroutines.delay
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.combine
@@ -157,6 +158,27 @@ class NostrClient(
                 false,
             )
 
+    /**
+     * Periodically wakes up disconnected relays. Without this, a relay
+     * that hit a long backoff (5 min, e.g. host unreachable or a server
+     * error code) would stay disconnected forever in the absence of any
+     * subscription change. The per-relay [BasicRelayClient] backoff still
+     * gates the actual reconnect attempt, so dead relays are not hammered.
+     */
+    private val keepAliveJob =
+        scope.launch {
+            while (true) {
+                delay(KEEP_ALIVE_INTERVAL_MS)
+                if (this@NostrClient.isActive) {
+                    relayPool.reconnectIfNeedsTo(ignoreRetryDelays = false)
+                }
+            }
+        }
+
+    companion object {
+        private const val KEEP_ALIVE_INTERVAL_MS = 60_000L
+    }
+
     override fun reconnect(
         onlyIfChanged: Boolean,
         ignoreRetryDelays: Boolean,