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/WorkerBootstrap.md

@@ -1,13 +1,13 @@
 # Worker Bootstrap
 
-The bootstrap layer parses the command-line arguments and environment variables passed to the `MxGateway.Worker` process, validates them against the gateway contract, and produces either a populated `WorkerOptions` instance or a structured failure that maps to a `WorkerExitCode`.
+The bootstrap layer parses the command-line arguments and environment variables passed to the `ZB.MOM.WW.MxGateway.Worker` process, validates them against the gateway contract, and produces either a populated `WorkerOptions` instance or a structured failure that maps to a `WorkerExitCode`.
 
 ## Overview
 
 The worker process is a short-lived child of the gateway. The gateway side of this contract lives in [WorkerProcessLauncher](./WorkerProcessLauncher.md). On the worker side, `Program.cs` is a single line that delegates to `WorkerApplication.Run(args)`:
 
 ```csharp
-using MxGateway.Worker;
+using ZB.MOM.WW.MxGateway.Worker;
 
 return WorkerApplication.Run(args);
 ```