feat: wire SQLite replication between site nodes and fix ConfigurationDatabase tests

Add SiteReplicationActor (runs on every site node) to replicate deployed
configs and store-and-forward buffer operations to the standby peer via
cluster member discovery and fire-and-forget Tell. Wire ReplicationService
handler and pass replication actor to DeploymentManagerActor singleton.

Fix 5 pre-existing ConfigurationDatabase test failures: RowVersion NOT NULL
on SQLite, stale migration name assertion, and seed data count mismatch.

src/ScadaLink.Commons/Interfaces/Services/IExternalSystemClient.cs

@@ -1,3 +1,5 @@
+using ScadaLink.Commons.Types;
+
 namespace ScadaLink.Commons.Interfaces.Services;
 
 /// <summary>
@@ -34,4 +36,27 @@ public record ExternalCallResult(
     bool Success,
     string? ResponseJson,
     string? ErrorMessage,
-    bool WasBuffered = false);
+    bool WasBuffered = false)
+{
+    private dynamic? _response;
+    private bool _responseParsed;
+
+    /// <summary>
+    /// Parsed response as a dynamic object. Returns null if ResponseJson is null or empty.
+    /// Access properties directly: result.Response.result, result.Response.items[0].name, etc.
+    /// </summary>
+    public dynamic? Response
+    {
+        get
+        {
+            if (!_responseParsed)
+            {
+                _response = string.IsNullOrEmpty(ResponseJson)
+                    ? null
+                    : new DynamicJsonElement(System.Text.Json.JsonDocument.Parse(ResponseJson).RootElement);
+                _responseParsed = true;
+            }
+            return _response;
+        }
+    }
+}