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>

docs/WorkerSta.md

@@ -4,7 +4,7 @@ The worker STA runtime owns the dedicated single-threaded apartment thread that
 
 ## Why an STA Is Required
 
-The installed MXAccess interop assembly declares an `Apartment` threading model (see `gateway.md` under "STA Worker Thread Model"). COM objects with that model must be created and called on a thread initialized as a single-threaded apartment, and any callbacks the object raises (event sink calls) are delivered through the thread's Windows message queue. A plain blocking queue is not sufficient: the STA loop must pump Windows messages so that the COM marshaler can deliver event invocations on the same thread that holds the object. Because of that constraint, every MXAccess operation in the worker is funneled through the types in `src/MxGateway.Worker/Sta/`.
+The installed MXAccess interop assembly declares an `Apartment` threading model (see `gateway.md` under "STA Worker Thread Model"). COM objects with that model must be created and called on a thread initialized as a single-threaded apartment, and any callbacks the object raises (event sink calls) are delivered through the thread's Windows message queue. A plain blocking queue is not sufficient: the STA loop must pump Windows messages so that the COM marshaler can deliver event invocations on the same thread that holds the object. Because of that constraint, every MXAccess operation in the worker is funneled through the types in `src/ZB.MOM.WW.MxGateway.Worker/Sta/`.
 
 ## Types
 
@@ -20,13 +20,13 @@ The installed MXAccess interop assembly declares an `Apartment` threading model
 
 ## STA Thread Initialization
 
-`StaRuntime`'s constructor configures a background `Thread` named `MxGateway.Worker.STA` and forces it into `ApartmentState.STA` before the thread starts. `Start()` releases the thread and then blocks on `startedEvent` so callers observe a fully-initialized apartment (or a captured `startupException`) before the first `InvokeAsync` call:
+`StaRuntime`'s constructor configures a background `Thread` named `ZB.MOM.WW.MxGateway.Worker.STA` and forces it into `ApartmentState.STA` before the thread starts. `Start()` releases the thread and then blocks on `startedEvent` so callers observe a fully-initialized apartment (or a captured `startupException`) before the first `InvokeAsync` call:
 
 ```csharp
 staThread = new Thread(ThreadMain)
 {
     IsBackground = true,
-    Name = "MxGateway.Worker.STA"
+    Name = "ZB.MOM.WW.MxGateway.Worker.STA"
 };
 staThread.SetApartmentState(ApartmentState.STA);
 ```