review(Cluster): record findings + fix snapshot consistency, dispose, stale docs

Code review at HEAD 7286d320. Cluster-001 (SeedFromCurrentState reads from one
snapshot), Cluster-003 (HoconLoader double-dispose), Cluster-004 (stale akka.conf
header), Cluster-005 (ServiceLevelCalculator tests added to Cluster.Tests). Cluster-002
deferred (no production caller).

src/Core/ZB.MOM.WW.OtOpcUa.Cluster/ClusterRoleInfo.cs

@@ -99,7 +99,7 @@ public sealed class ClusterRoleInfo : IClusterRoleInfo, IDisposable
 
             foreach (var role in snapshot.Members.SelectMany(m => m.Roles).Distinct())
             {
-                var leaderAddr = _cluster.State.RoleLeader(role);
+                var leaderAddr = snapshot.RoleLeader(role);
                 _roleLeaders[role] = leaderAddr is not null
                     ? snapshot.Members.FirstOrDefault(m => m.Address == leaderAddr)
                     : null;

src/Core/ZB.MOM.WW.OtOpcUa.Cluster/HoconLoader.cs

@@ -9,10 +9,10 @@ public static class HoconLoader
     /// <returns>The loaded HOCON configuration as a string.</returns>
     public static string LoadBaseConfig()
     {
-        using var stream = typeof(HoconLoader).Assembly.GetManifestResourceStream(ResourceName)
-            ?? throw new InvalidOperationException(
-                $"Embedded resource '{ResourceName}' not found. Verify EmbeddedResource glob in csproj.");
-        using var reader = new StreamReader(stream);
+        using var reader = new StreamReader(
+            typeof(HoconLoader).Assembly.GetManifestResourceStream(ResourceName)
+                ?? throw new InvalidOperationException(
+                    $"Embedded resource '{ResourceName}' not found. Verify EmbeddedResource glob in csproj."));
         return reader.ReadToEnd();
     }
 }

src/Core/ZB.MOM.WW.OtOpcUa.Cluster/Resources/akka.conf

@@ -1,11 +1,10 @@
 # Base Akka.NET cluster configuration for OtOpcUa fused-host nodes.
 #
 # Roles, seed nodes, public hostname/port, and the actor system name are overlaid
-# at runtime by AkkaHostedService — see ZB.MOM.WW.OtOpcUa.Cluster/AkkaHostedService.cs.
+# at runtime by ServiceCollectionExtensions.WithOtOpcUaClusterBootstrap (via Akka.Hosting).
 # Everything else here is the cluster-wide tuning that should match across nodes.
 #
-# Tuning sourced from ScadaLink (ScadaLink.Host/Actors/AkkaHostedService.BuildHocon);
-# any divergence must be deliberate and recorded in docs/v2/Architecture.md.
+# Any divergence from these defaults must be deliberate and recorded in docs/v2/Architecture.md.
 
 akka {
     extensions = [