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.Server/Sessions/ISessionRegistry.cs

@@ -0,0 +1,48 @@
+using System.Diagnostics.CodeAnalysis;
+
+namespace ZB.MOM.WW.MxGateway.Server.Sessions;
+
+/// <summary>
+/// Registry for managing active gateway sessions.
+/// </summary>
+public interface ISessionRegistry
+{
+    /// <summary>
+    /// Total number of sessions (open or closed) in the registry.
+    /// </summary>
+    int Count { get; }
+
+    /// <summary>
+    /// Number of sessions currently in an active (open) state.
+    /// </summary>
+    int ActiveCount { get; }
+
+    /// <summary>
+    /// Attempts to add a session to the registry; returns false if session ID already exists.
+    /// </summary>
+    /// <param name="session">Session to add.</param>
+    /// <returns>True if added; false if session ID already exists.</returns>
+    bool TryAdd(GatewaySession session);
+
+    /// <summary>
+    /// Attempts to retrieve a session by ID; returns false if not found.
+    /// </summary>
+    /// <param name="sessionId">Identifier of the session.</param>
+    /// <param name="session">The retrieved session, if found.</param>
+    /// <returns>True if found; false otherwise.</returns>
+    bool TryGet(string sessionId, [MaybeNullWhen(false)] out GatewaySession session);
+
+    /// <summary>
+    /// Attempts to remove a session by ID; returns false if not found.
+    /// </summary>
+    /// <param name="sessionId">Identifier of the session to remove.</param>
+    /// <param name="session">The removed session, if found.</param>
+    /// <returns>True if removed; false if not found.</returns>
+    bool TryRemove(string sessionId, [MaybeNullWhen(false)] out GatewaySession session);
+
+    /// <summary>
+    /// Returns a snapshot of all sessions in the registry.
+    /// </summary>
+    /// <returns>A read-only collection of all sessions.</returns>
+    IReadOnlyCollection<GatewaySession> Snapshot();
+}