fix(dcl): push tag-resolution counts on first subscribe (register row 55)

A site health report showed tagResolutionCounts 0/0 for a connection whose
dataConnectionTagQuality on the SAME report read good:2 — reproduced live on
the docker rig against site-a's rig-probe-1 instance (2 Good OPC UA tags on
"OPC PLC Simulator"), on the ACTIVE node's own report.

Not a standby-shadowing or keying/removal problem, and not a serialization
problem: both dictionaries live on one collector instance on one node, and the
CentralControlDtoMapper round-trip is correct in both directions. The actor's
own derived counts (TotalSubscribedTagCount / ResolvedTagCount) were right the
whole time — GetHealthReport replied 2/2.

Root cause: HandleSubscribeCompleted — the path that registers tags on a first,
healthy subscribe — mutated _instancesByTag and _subscriptionIds but never
pushed to ISiteHealthCollector. The only pushes were BecomeConnected's (fires
before any instance subscribes, so its 0/0 is legitimate), the batch apply
(reconnect re-subscribe / resolution probe) and unsubscribe (teardown). A
connection whose tags all resolve first time reaches none of those, and
ScheduleTagResolutionRetry cancels the retry timer outright when nothing is
unresolved — so the connect-time 0/0 was never superseded and stood forever.

The blind spot was therefore worst on a perfectly healthy connection, which is
exactly when the "device still booting / tag path unresolved" diagnostic should
read clean rather than empty. Any reconnect masked it (the batch path pushes),
which is why it presented only on a clean first deploy.

Fix: push the derived counts at the end of the first-subscribe apply, mirroring
the existing push site in HandleBatchSubscribeCompleted. No semantic change to
the null/no-data convention — the map entry already existed, its values were
simply stale zeros.

Tests: fail-before regression test pins the exact mechanism (NSubstitute records
a single UpdateTagResolution(name, 0, 0) pre-fix while the actor reports 2/2).
DCL 320, HealthMonitoring 97, SiteRuntime 605, Communication 717 all green;
slnx builds clean.

Docs: Component-DataConnectionLayer.md said the counts were "derived at report
time", which implies a pull that cannot go stale and papered over this bug.
Corrected to state they are pushed, name the four push sites, and record why a
healthy connection was the worst case.

tests/ZB.MOM.WW.ScadaBridge.DataConnectionLayer.Tests/DataConnectionActorTests.cs

@@ -1770,4 +1770,61 @@ public class DataConnectionActorTests : TestKit
         // Belt-and-braces: after the fresh value, no further (stale) update may arrive.
         ExpectNoMsg(TimeSpan.FromMilliseconds(500));
     }
+
+    // ── Deferred register row 55: first-subscribe resolution counts never reached the collector ──
+
+    [Fact]
+    public async Task FirstSubscribe_AllTagsResolve_PushesResolutionCountsToHealthCollector()
+    {
+        // Regression test for deferred-work register row 55, reproduced live on the docker
+        // rig: site-a's health report showed
+        //   tagResolutionCounts = { "OPC PLC Simulator": { totalSubscribed: 0, resolved: 0 } }
+        // while dataConnectionTagQuality on the SAME report (same collector, same active
+        // node) said good: 2.
+        //
+        // Mechanism: the ONLY health push on the happy path was BecomeConnected's, which
+        // fires BEFORE any instance has subscribed and is therefore a legitimate 0/0.
+        // HandleSubscribeCompleted — the path that registers tags on a first, healthy
+        // subscribe — mutated _instancesByTag and _subscriptionIds but pushed nothing, so
+        // that 0/0 was never superseded. The two sites that DO push are
+        // HandleBatchSubscribeCompleted (reconnect re-subscribe / resolution probe) and
+        // HandleUnsubscribe (teardown); neither runs on a connection whose tags all
+        // resolve first time, and ScheduleTagResolutionRetry cancels the retry timer
+        // outright when _unresolvedTags is empty. Result: a fully healthy connection
+        // reported 0/0 forever, blinding the "device still booting / tag path unresolved"
+        // diagnostic exactly when it is supposed to read clean.
+        //
+        // The actor's OWN derived counts were correct the whole time — that asymmetry is
+        // the signature of the bug, so this test pins both halves.
+        _mockAdapter.ConnectAsync(Arg.Any<IDictionary<string, string>>(), Arg.Any<CancellationToken>())
+            .Returns(Task.CompletedTask);
+        _mockAdapter.Status.Returns(ConnectionHealth.Connected);
+        _mockAdapter.SubscribeAsync(Arg.Any<string>(), Arg.Any<SubscriptionCallback>(), Arg.Any<CancellationToken>())
+            .Returns(ci => Task.FromResult("sub-" + ci.ArgAt<string>(0)));
+        _mockAdapter.ReadAsync(Arg.Any<string>(), Arg.Any<CancellationToken>())
+            .Returns(new ReadResult(false, null, null));
+
+        var actor = CreateConnectionActor("row55-first-subscribe");
+        await Task.Delay(300);
+
+        // BecomeConnected has now pushed its legitimate 0/0 (no tags subscribed yet).
+        _mockHealthCollector.Received().UpdateTagResolution("row55-first-subscribe", 0, 0);
+
+        // One instance subscribes to two tags; both resolve on the first attempt, so the
+        // batch/probe path never runs — exactly the rig's rig-probe-1 shape.
+        actor.Tell(new SubscribeTagsRequest(
+            "c1", "inst1", "row55-first-subscribe",
+            ["sensor/temp", "sensor/pressure"], DateTimeOffset.UtcNow));
+        ExpectMsg<SubscribeTagsResponse>(TimeSpan.FromSeconds(5));
+
+        // The actor's own derived counts are correct — this half passed pre-fix too.
+        actor.Tell(new DataConnectionActor.GetHealthReport());
+        var report = ExpectMsg<DataConnectionHealthReport>(TimeSpan.FromSeconds(5));
+        Assert.Equal(2, report.TotalSubscribedTags);
+        Assert.Equal(2, report.ResolvedTags);
+
+        // The collector must agree. Pre-fix this is the failing assertion: the only call
+        // ever recorded was the (0, 0) from BecomeConnected.
+        _mockHealthCollector.Received().UpdateTagResolution("row55-first-subscribe", 2, 2);
+    }
 }