feat(siteeventlog): emit script started/completed Info events (M1.8)

ScriptExecutionActor previously emitted only an Error 'script' event on failure.
It now also fire-and-forgets an Info 'script' event when execution starts (right
before RunAsync) and when it completes successfully — giving the operational log
the full started/completed/failed lifecycle. Uses the already-resolved
siteEventLogger; fire-and-forget so the event log can never block or fault the
script's own run.

Extends the SingleServiceProvider test helper to also serve IServiceScopeFactory
(returning a self-scope) so ScriptExecutionActor's serviceProvider.CreateScope()
reaches the logging hot path in tests instead of throwing into the catch.

src/ZB.MOM.WW.ScadaBridge.SiteRuntime/Actors/ScriptExecutionActor.cs

@@ -217,6 +217,13 @@ public class ScriptExecutionActor : ReceiveActor
                     Scope = scope
                 };
 
+                // M1.8: operational `script` event — execution started. Fire-and-forget
+                // (the `_ =` discards the task) so the event log can never block or
+                // fault the script's own run; mirrors the existing Error-path emit.
+                _ = siteEventLogger?.LogEventAsync(
+                    "script", "Info", instanceName, $"ScriptActor:{scriptName}",
+                    $"Script '{scriptName}' on instance '{instanceName}' started");
+
                 var state = await compiledScript.RunAsync(globals, cts.Token);
 
                 // Send result to requester if this was an Ask-based call
@@ -225,6 +232,11 @@ public class ScriptExecutionActor : ReceiveActor
                     replyTo.Tell(new ScriptCallResult(correlationId, true, state.ReturnValue, null));
                 }
 
+                // M1.8: operational `script` event — execution completed successfully.
+                _ = siteEventLogger?.LogEventAsync(
+                    "script", "Info", instanceName, $"ScriptActor:{scriptName}",
+                    $"Script '{scriptName}' on instance '{instanceName}' completed");
+
                 // Notify parent of completion
                 parent.Tell(new ScriptActor.ScriptExecutionCompleted(scriptName, true, null));
             }