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.Tests/TestSupport/RecordingServerStreamWriter.cs

@@ -0,0 +1,50 @@
+using Grpc.Core;
+
+namespace ZB.MOM.WW.MxGateway.Tests.TestSupport;
+
+/// <summary>
+/// Thread-safe <see cref="IServerStreamWriter{T}"/> that records every written message
+/// and lets a test await the first message with a timeout.
+/// </summary>
+/// <typeparam name="T">The streamed message type.</typeparam>
+public sealed class RecordingServerStreamWriter<T> : IServerStreamWriter<T>
+{
+    private readonly object _syncRoot = new();
+    private readonly TaskCompletionSource<T> _firstMessage = new(TaskCreationOptions.RunContinuationsAsynchronously);
+    private readonly List<T> _messages = [];
+
+    /// <summary>Gets the messages written to this stream, in order.</summary>
+    public IReadOnlyList<T> Messages
+    {
+        get
+        {
+            lock (_syncRoot)
+            {
+                return _messages.ToArray();
+            }
+        }
+    }
+
+    /// <summary>Gets or sets options for writing messages to the stream.</summary>
+    public WriteOptions? WriteOptions { get; set; }
+
+    /// <summary>Records the supplied message.</summary>
+    /// <param name="message">The message to record.</param>
+    /// <returns>A completed task.</returns>
+    public Task WriteAsync(T message)
+    {
+        lock (_syncRoot)
+        {
+            _messages.Add(message);
+        }
+
+        _firstMessage.TrySetResult(message);
+        return Task.CompletedTask;
+    }
+
+    /// <summary>Waits for the first message to be written within the specified timeout.</summary>
+    /// <param name="timeout">Maximum time to wait for the first message.</param>
+    /// <returns>The first message written to this stream.</returns>
+    public async Task<T> WaitForFirstMessageAsync(TimeSpan timeout) =>
+        await _firstMessage.Task.WaitAsync(timeout).ConfigureAwait(false);
+}