feat(telemetry): deploy-failure, S&F activity, script-run and DCL-transition instruments (ScadaBridge#81)

Adds four instruments on the already-allow-listed ZB.MOM.WW.ScadaBridge meter:
scadabridge.deployments.failed{reason}, scadabridge.store_and_forward.activity{action,category},
scadabridge.site.script.runs{outcome} + scadabridge.site.script.duration{outcome} (ms),
scadabridge.site.data_connections.transitions{state}. Queue depth, DCL connection state and
deploy-applied already existed. No new Meter, so ZbTelemetryOptions.Meters needs no change.

Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV

tests/ZB.MOM.WW.ScadaBridge.StoreAndForward.Tests/QueueDepthGaugeTests.cs

@@ -97,6 +97,43 @@ public class QueueDepthGaugeTests : IAsyncLifetime, IDisposable
         return observed;
     }
 
+    /// <summary>
+    /// ScadaBridge#81: the service emits <c>scadabridge.store_and_forward.activity</c> for a buffered
+    /// message (Queued) and for a message that exhausts its retries (Parked), through the real service.
+    /// </summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
+    [Fact]
+    public async Task ActivityCounter_IsEmitted_ForQueuedAndParked()
+    {
+        var seen = new System.Collections.Concurrent.ConcurrentQueue<string>();
+        using var listener = new MeterListener
+        {
+            InstrumentPublished = (i, l) =>
+            {
+                if (i.Meter.Name == ScadaBridgeTelemetry.MeterName
+                    && i.Name == "scadabridge.store_and_forward.activity")
+                    l.EnableMeasurementEvents(i);
+            }
+        };
+        listener.SetMeasurementEventCallback<long>((_, _, tags, _) =>
+        {
+            foreach (var t in tags)
+                if (t.Key == "action" && t.Value is string a) seen.Enqueue(a);
+        });
+        listener.Start();
+
+        _service.RegisterDeliveryHandler(StoreAndForwardCategory.ExternalSystem,
+            _ => throw new HttpRequestException("transient"));
+
+        var r = await _service.EnqueueAsync(
+            StoreAndForwardCategory.ExternalSystem, "api-activity", """{}""", maxRetries: 1);
+        Assert.True(r.WasBuffered);
+        await _service.RetryPendingMessagesAsync();
+
+        Assert.Contains("Queued", seen);
+        Assert.Contains("Parked", seen);
+    }
+
     /// <summary>
     /// Review 2026-10-21 02/C3: rows that arrive without passing through this node's counter
     /// paths (LocalDb CDC on a standby) are picked up by the sweep's periodic re-seed.