feat(historian): backend registry, ServerHistorian:Backend, Host wiring via provider

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

src/Server/ZB.MOM.WW.OtOpcUa.Host/Program.cs

@@ -229,11 +229,21 @@ if (hasDriver)
     if (builder.Configuration.GetValue<bool>("AlarmHistorian:Enabled") && !serverHistorianOptions.Enabled)
         Log.Warning(
             "AlarmHistorian is enabled but ServerHistorian is disabled — the alarm-history sink is sourcing its " +
-            "gateway connection (endpoint/key/TLS) from the disabled ServerHistorian section; HistoryReads stay GoodNoData.");
+            "{Backend} backend connection from the disabled ServerHistorian section; HistoryReads stay GoodNoData.",
+            serverHistorianOptions.Backend);
+
+    // Backend selection: resolve the provider once (unknown name => OptionsValidationException naming the
+    // allowed values) and build every historian seam through it.
+    var historianProvider = HistorianBackendRegistry.Resolve(serverHistorianOptions, builder.Configuration);
+    builder.Services.AddSingleton<IHistorianBackendProvider>(historianProvider);
+    // HistoryUpdate is gated like HistoryRead: None unconditionally, the real holder only when enabled.
+    builder.Services.AddSingleton(HistorianUpdaterHolder.None);
+    if (serverHistorianOptions.Enabled)
+        builder.Services.AddSingleton(sp => new HistorianUpdaterHolder(historianProvider.CreateUpdater(sp)));
 
     builder.Services.AddAlarmHistorian(
         builder.Configuration,
-        (_, sp) => GatewayHistorian.CreateAlarmWriter(serverHistorianOptions, sp));
+        (_, sp) => historianProvider.CreateAlarmWriter(sp));
 
     // Node-local LocalDb: caches the deployed-configuration artifact so this node can boot from
     // its last-known-good config when central SQL is unreachable, and optionally replicates that
@@ -260,7 +270,7 @@ if (hasDriver)
     // and the ServerHistorianOptions -> client-options mapping); Runtime owns the gating.
     builder.Services.AddServerHistorian(
         builder.Configuration,
-        (opts, sp) => GatewayHistorian.CreateDataSource(opts, sp));
+        (_, sp) => historianProvider.CreateDataSource(sp));
 
     // Config-gated historian tag provisioning. When the ServerHistorian section is enabled this registers the
     // gateway-backed GatewayTagProvisioner (overriding the NullHistorianProvisioning default) so that deploying
@@ -271,7 +281,7 @@ if (hasDriver)
     // ServerHistorian:Enabled flag as the read path — both target the same single gateway.
     builder.Services.AddHistorianProvisioning(
         builder.Configuration,
-        (opts, sp) => GatewayHistorian.CreateProvisioner(opts, sp));
+        (_, sp) => historianProvider.CreateProvisioning(sp));
 
     // Continuous historization of driver (non-Galaxy) tag values. Gated on ContinuousHistorization:Enabled
     // AND the ServerHistorian gateway being configured: the recorder drains driver-tag live values to the
@@ -309,11 +319,7 @@ if (hasDriver)
 
         // Gateway-backed live-value writer over its OWN gRPC channel to the same single gateway (a second
         // channel to a co-located sidecar is cheap — the gateway pools the historian sessions server-side).
-        builder.Services.AddSingleton<IHistorianValueWriter>(sp =>
-            new GatewayHistorianValueWriter(
-                HistorianGatewayClientAdapter.Create(
-                    serverHistorianOptions, sp.GetRequiredService<ILoggerFactory>()),
-                sp.GetRequiredService<ILogger<GatewayHistorianValueWriter>>()));
+        builder.Services.AddSingleton<IHistorianValueWriter>(sp => historianProvider.CreateValueWriter(sp));
     }
 
     // Bind every cross-platform driver factory before AddAkka resolves IDriverFactory — replaces