rename: prefix gateway projects/namespaces with ZB.MOM.WW + sln→slnx

Apply the ZB.MOM.WW. prefix to all gateway-side projects, folders,
.csproj/.sln contents, C# namespaces, using directives, generated proto
C# (csharp_namespace + checked-in generated files), InternalsVisibleTo
attributes, project-name string literals (LoadProject, .sln lookups,
worker exe paths, staticwebassets manifest), and the install/script/doc
references that point at any of the above. Migrate the solution from
.sln to .slnx via `dotnet sln migrate` and delete the old file.

External-runtime identifiers are intentionally NOT prefixed so external
configuration keeps working:
- GatewayMetrics.cs MeterName ("MxGateway.Server")
- DashboardAuthenticationDefaults Scheme/Policy ("MxGateway.Dashboard")
- GatewayRequestLoggingMiddleware logger category ("MxGateway.Request")
- StaRuntime thread name ("MxGateway.Worker.STA")
- appsettings.json root section "MxGateway" + env-var prefix
  MxGateway__... and secret-name MxGateway:ApiKeyPepper
- C:\ProgramData\MxGateway\ data dir paths

Also fixes two tests that were not rename-related but became visible
while validating the rename:

- WorkerLiveMxAccessSmokeTests.ShutDownAsync: cancellation that the
  gateway service correctly maps to RpcException(Cancelled) per gRPC
  convention was being misclassified as a stream fault. Added a sibling
  catch on RpcException with StatusCode.Cancelled.

- IntegrationTestEnvironment.ResolveRepositoryRoot: extracted IsRepositoryRoot
  and made it accept either a .git marker OR a .sln/.slnx next to src/
  so the worker-exe walker works in non-git working copies.

clients/proto/proto-inputs.json's protoRoot updated to point at
src/ZB.MOM.WW.MxGateway.Contracts/Protos.

Verified by `dotnet build` and a full `dotnet test` of the .slnx with
MXGATEWAY_RUN_LIVE_{MXACCESS,LDAP,GALAXY}_TESTS=1:
  Tests: 472/472 pass
  Worker.Tests: 280/280 pass (4 dev-rig [Fact(Skip=...)] skipped)
  IntegrationTests: 18/18 pass

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

src/ZB.MOM.WW.MxGateway.Worker/MxAccess/WorkerRuntimeHeartbeatSnapshot.cs

@@ -0,0 +1,41 @@
+using System;
+
+namespace ZB.MOM.WW.MxGateway.Worker.MxAccess;
+
+public sealed class WorkerRuntimeHeartbeatSnapshot
+{
+    /// <summary>Initializes a new instance of the <see cref="WorkerRuntimeHeartbeatSnapshot"/> class.</summary>
+    /// <param name="lastStaActivityUtc">Timestamp of the last STA thread activity in UTC.</param>
+    /// <param name="pendingCommandCount">Number of commands awaiting processing.</param>
+    /// <param name="outboundEventQueueDepth">Current depth of the worker event queue.</param>
+    /// <param name="lastEventSequence">Sequence number of the most recent event.</param>
+    /// <param name="currentCommandCorrelationId">Correlation ID of the in-flight command.</param>
+    public WorkerRuntimeHeartbeatSnapshot(
+        DateTimeOffset lastStaActivityUtc,
+        uint pendingCommandCount,
+        uint outboundEventQueueDepth,
+        ulong lastEventSequence,
+        string currentCommandCorrelationId)
+    {
+        LastStaActivityUtc = lastStaActivityUtc;
+        PendingCommandCount = pendingCommandCount;
+        OutboundEventQueueDepth = outboundEventQueueDepth;
+        LastEventSequence = lastEventSequence;
+        CurrentCommandCorrelationId = currentCommandCorrelationId ?? string.Empty;
+    }
+
+    /// <summary>Gets the last STA activity timestamp in UTC.</summary>
+    public DateTimeOffset LastStaActivityUtc { get; }
+
+    /// <summary>Gets the pending command count.</summary>
+    public uint PendingCommandCount { get; }
+
+    /// <summary>Gets the current depth of the worker event queue.</summary>
+    public uint OutboundEventQueueDepth { get; }
+
+    /// <summary>Gets the sequence number of the most recent event.</summary>
+    public ulong LastEventSequence { get; }
+
+    /// <summary>Gets the correlation ID of the in-flight command.</summary>
+    public string CurrentCommandCorrelationId { get; }
+}