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/Host.md

@@ -87,13 +87,15 @@ public bool IsActiveNode
 
 `Program.cs` (Central branch) calls `WebApplication.CreateBuilder`, registers shared and central-only components, builds the `WebApplication`, applies or retries database migrations, and mounts the middleware pipeline and endpoints. The order is intentional: `UseAuthentication` and `UseAuthorization` run before `UseAuditWriteMiddleware` so `HttpContext.User` is populated when the audit row is written.
 
+Before branching on role, `AkkaHostedService.StartAsync` creates one actor unconditionally on every node:
+- `DeadLetterMonitorActor` — plain `ActorOf`; subscribes to the `DeadLetter` event stream on `PreStart`. Runs on both central and site nodes.
+
 `AkkaHostedService.RegisterCentralActors` creates:
 - `CentralCommunicationActor` — registered with `ClusterClientReceptionist` so site `ClusterClient`s can reach it.
 - `ManagementActor` — also registered with `ClusterClientReceptionist`; the CLI connects via `ClusterClient` without joining the cluster.
 - `NotificationOutboxActor` — cluster singleton (no role scope); a proxy is handed to `CentralCommunicationActor` so forwarded `NotificationSubmit` messages from sites are routed to it.
 - `AuditLogIngestActor` — cluster singleton; proxy registered with both `CentralCommunicationActor` and (if present) the `SiteStreamGrpcServer`.
 - `SiteCallAuditActor` — cluster singleton; a graceful-stop task is added to the `cluster-leave` coordinated-shutdown phase with a 10-second drain window.
-- `DeadLetterMonitorActor` — plain `ActorOf`; subscribes to the `DeadLetter` event stream on `PreStart`.
 
 ### Site composition root
 
@@ -132,10 +134,10 @@ The Host is not consumed as a library; it is the executable entry point. Other c
 
 | Component | Central | Site | `AddXxx` | Actors | `MapXxx` |
 |---|:---:|:---:|:---:|:---:|:---:|
-| ClusterInfrastructure | Yes | Yes | Yes | Yes | — |
+| ClusterInfrastructure | Yes | Yes | Yes | — | — |
 | Communication | Yes | Yes | Yes | Yes | — |
-| HealthMonitoring | Yes | Yes | Yes | Yes | — |
-| ExternalSystemGateway | Yes | Yes | Yes | Yes | — |
+| HealthMonitoring | Yes | Yes | Yes | — | — |
+| ExternalSystemGateway | Yes | Yes | Yes | — | — |
 | AuditLog | Yes | Yes | Yes | Yes | — |
 | NotificationService | Yes | No | Yes | — | — |
 | NotificationOutbox | Yes | No | Yes | Yes (singleton) | — |
@@ -176,7 +178,7 @@ Options are bound via the .NET Options pattern (`IOptions<T>`). Each component o
 | Key | Default | Description |
 |-----|---------|-------------|
 | `SeedNodes` | — | List of Akka seed-node URIs (`akka.tcp://scadabridge@host:port`). At least 2 required. Must reference remoting ports, not gRPC ports. |
-| `SplitBrainResolverStrategy` | — | Active strategy name (e.g. `"keep-oldest"`). |
+| `SplitBrainResolverStrategy` | `keep-oldest` | Active strategy name (e.g. `"keep-oldest"`). |
 | `StableAfter` | `"00:00:15"` | Duration the cluster must be stable before the resolver acts. |
 | `HeartbeatInterval` | `"00:00:02"` | Akka failure-detector heartbeat cadence. |
 | `FailureDetectionThreshold` | `"00:00:10"` | Acceptable heartbeat pause before a node is considered unreachable. |