docs(components): accuracy fixes from deep review (batch 1)

Commons (third-party dep, 7 namespaces, retired ApiKey, repo SaveChanges
carve-out), ConfigurationDatabase (5 persisted + 1 non-persisted computed col),
ClusterInfrastructure (abbreviated HOCON note, RemotingPort default),
Host (component matrix: CI/HealthMonitoring/ExternalSystemGateway have no
actors; DeadLetterMonitorActor runs on both roles), Security (Bearer not
X-API-Key; ApiKeyAdmin registered by Host), Communication (Task.Run/Sender).

docs/components/Communication.md

@@ -96,7 +96,7 @@ _centralClient.Tell(
     new ClusterClient.Send("/user/central-communication", msg), Sender);
 ```
 
-The original `Sender` is forwarded as the `ClusterClient.Send` sender so any reply from central routes straight back to the waiting Ask on the site, not through `SiteCommunicationActor`.
+For request/response messages, the original `Sender` is forwarded as the `ClusterClient.Send` sender so any reply from central routes straight back to the waiting Ask on the site, not through `SiteCommunicationActor`. For fire-and-forget messages (e.g. `SiteHealthReport`), `Self` is used as the sender instead, because no reply is expected.
 
 ### Address loading and the 60-second refresh
 
@@ -145,7 +145,7 @@ private void HandleAttributeValueChanged(AttributeValueChanged msg)
 **Central-side** — `SiteStreamGrpcClient` / `SiteStreamGrpcClientFactory`:
 
 - `SiteStreamGrpcClientFactory` (singleton) caches one `SiteStreamGrpcClient` per site identifier. On `GetOrCreate`, it compares the cached client's `Endpoint` to the requested endpoint and atomically replaces a stale client (different endpoint — NodeA→NodeB failover flip, or an edited address) with a fresh one.
-- `SiteStreamGrpcClient` opens a `GrpcChannel` with HTTP/2 keepalive (`KeepAlivePingDelay` default 15 s, `KeepAlivePingTimeout` default 10 s, `KeepAlivePingPolicy.Always`). It calls `SubscribeInstance` and reads the response stream in a background `Task.Run`, invoking `onEvent` for each received event and `onError` on any non-cancellation exception.
+- `SiteStreamGrpcClient` opens a `GrpcChannel` with HTTP/2 keepalive (`KeepAlivePingDelay` default 15 s, `KeepAlivePingTimeout` default 10 s, `KeepAlivePingPolicy.Always`). `SubscribeAsync` is a plain `async Task` that calls `SubscribeInstance` and reads the response stream with `await foreach`, invoking `onEvent` for each received event and `onError` on any non-cancellation exception. The caller (`DebugStreamBridgeActor.OpenGrpcStream`) launches it inside a `Task.Run` so the long-running stream loop runs off the actor thread.
 
 ### Debug stream session lifecycle