fix(store-and-forward): resolve S&F delivery + replication wiring (3 Critical findings)

Resolves StoreAndForward-001, ExternalSystemGateway-001, NotificationService-001
— one systemic gap where buffered messages were persisted but never delivered,
and the active node never replicated its buffer to the standby.

Delivery handlers (ExternalSystemGateway-001 / NotificationService-001):
- AkkaHostedService registers delivery handlers for the ExternalSystem,
  CachedDbWrite and Notification categories after StoreAndForwardService starts;
  each resolves its scoped consumer in a fresh DI scope.
- ExternalSystemClient, DatabaseGateway and NotificationDeliveryService each
  gain a DeliverBufferedAsync method: re-resolve the target and re-attempt
  delivery, returning true/false/throwing per the transient-vs-permanent contract.
- EnqueueAsync gains an attemptImmediateDelivery flag; CachedCallAsync and
  NotificationDeliveryService.SendAsync pass false (they already attempted
  delivery themselves) so registering a handler does not dispatch twice.

Replication (StoreAndForward-001):
- ReplicationService is injected into StoreAndForwardService; a new BufferAsync
  helper replicates every enqueue, and successful-retry removes and parks are
  replicated too. Fire-and-forget, no-op when replication is disabled.

Tests: StoreAndForwardReplicationTests (Add/Remove/Park observed),
attemptImmediateDelivery behaviour, and DeliverBufferedAsync paths for each
consumer. Full solution builds; StoreAndForward/ExternalSystemGateway/
NotificationService suites green.

src/ScadaLink.StoreAndForward/ServiceCollectionExtensions.cs

@@ -22,7 +22,8 @@ public static class ServiceCollectionExtensions
             var storage = sp.GetRequiredService<StoreAndForwardStorage>();
             var options = sp.GetRequiredService<IOptions<StoreAndForwardOptions>>().Value;
             var logger = sp.GetRequiredService<ILogger<StoreAndForwardService>>();
-            return new StoreAndForwardService(storage, options, logger);
+            var replication = sp.GetRequiredService<ReplicationService>();
+            return new StoreAndForwardService(storage, options, logger, replication);
         });
 
         services.AddSingleton<ReplicationService>(sp =>