chore: organize solution into module folders (Core/Server/Drivers/Client/Tooling)

Group all 69 projects into category subfolders under src/ and tests/ so the
Rider Solution Explorer mirrors the module structure. Folders: Core, Server,
Drivers (with a nested Driver CLIs subfolder), Client, Tooling.

- Move every project folder on disk with git mv (history preserved as renames).
- Recompute relative paths in 57 .csproj files: cross-category ProjectReferences,
  the lib/ HintPath+None refs in Driver.Historian.Wonderware, and the external
  mxaccessgw refs in Driver.Galaxy and its test project.
- Rebuild ZB.MOM.WW.OtOpcUa.slnx with nested solution folders.
- Re-prefix project paths in functional scripts (e2e, compliance, smoke SQL,
  integration, install).

Build green (0 errors); unit tests pass. Docs left for a separate pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/Server/ZB.MOM.WW.OtOpcUa.Admin.Tests/RedundancyMetricsTests.cs

@@ -0,0 +1,70 @@
+using System.Diagnostics.Metrics;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Admin.Services;
+
+namespace ZB.MOM.WW.OtOpcUa.Admin.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class RedundancyMetricsTests
+{
+    [Fact]
+    public void RecordRoleTransition_Increments_Counter_WithExpectedTags()
+    {
+        using var metrics = new RedundancyMetrics();
+        using var listener = new MeterListener();
+        var observed = new List<(long Value, Dictionary<string, object?> Tags)>();
+        listener.InstrumentPublished = (instrument, l) =>
+        {
+            if (instrument.Meter.Name == RedundancyMetrics.MeterName &&
+                instrument.Name == "otopcua.redundancy.role_transition")
+            {
+                l.EnableMeasurementEvents(instrument);
+            }
+        };
+        listener.SetMeasurementEventCallback<long>((_, value, tags, _) =>
+        {
+            var dict = new Dictionary<string, object?>();
+            foreach (var tag in tags) dict[tag.Key] = tag.Value;
+            observed.Add((value, dict));
+        });
+        listener.Start();
+
+        metrics.RecordRoleTransition("c1", "node-a", "Primary", "Secondary");
+
+        observed.Count.ShouldBe(1);
+        observed[0].Value.ShouldBe(1);
+        observed[0].Tags["cluster.id"].ShouldBe("c1");
+        observed[0].Tags["node.id"].ShouldBe("node-a");
+        observed[0].Tags["from_role"].ShouldBe("Primary");
+        observed[0].Tags["to_role"].ShouldBe("Secondary");
+    }
+
+    [Fact]
+    public void SetClusterCounts_Observed_Via_ObservableGauges()
+    {
+        using var metrics = new RedundancyMetrics();
+        metrics.SetClusterCounts("c1", primary: 1, secondary: 2, stale: 0);
+        metrics.SetClusterCounts("c2", primary: 0, secondary: 1, stale: 1);
+
+        var observations = new List<(string Name, long Value, string Cluster)>();
+        using var listener = new MeterListener();
+        listener.InstrumentPublished = (instrument, l) =>
+        {
+            if (instrument.Meter.Name == RedundancyMetrics.MeterName)
+                l.EnableMeasurementEvents(instrument);
+        };
+        listener.SetMeasurementEventCallback<long>((instrument, value, tags, _) =>
+        {
+            string? cluster = null;
+            foreach (var t in tags) if (t.Key == "cluster.id") cluster = t.Value as string;
+            observations.Add((instrument.Name, value, cluster ?? "?"));
+        });
+        listener.Start();
+        listener.RecordObservableInstruments();
+
+        observations.ShouldContain(o => o.Name == "otopcua.redundancy.primary_count" && o.Cluster == "c1" && o.Value == 1);
+        observations.ShouldContain(o => o.Name == "otopcua.redundancy.secondary_count" && o.Cluster == "c1" && o.Value == 2);
+        observations.ShouldContain(o => o.Name == "otopcua.redundancy.stale_count" && o.Cluster == "c2" && o.Value == 1);
+    }
+}