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/WorkerFrameProtocol.md

@@ -35,17 +35,22 @@ oversized frames, protocol version mismatches, and session mismatches.
 
 ## Verification
 
+The frame protocol lives in `ZB.MOM.WW.MxGateway.Worker.Ipc` (`WorkerFrameReader`,
+`WorkerFrameWriter`, `WorkerFrameProtocolOptions`) and is covered by
+`src/ZB.MOM.WW.MxGateway.Worker.Tests/Ipc/WorkerFrameProtocolTests.cs`. The worker is an
+x86 process, so build and test it with `-p:Platform=x86`.
+
 Run the focused tests after changing the frame protocol:
 
-```bash
-dotnet test src/MxGateway.Tests/MxGateway.Tests.csproj --filter WorkerFrameProtocolTests
+```powershell
+dotnet test src/ZB.MOM.WW.MxGateway.Worker.Tests/ZB.MOM.WW.MxGateway.Worker.Tests.csproj -p:Platform=x86 --filter WorkerFrameProtocolTests
 ```
 
-Run the gateway build because the frame protocol is part of
-`MxGateway.Server`:
+Run the x86 worker build because the frame protocol is part of
+`ZB.MOM.WW.MxGateway.Worker`:
 
-```bash
-dotnet build src/MxGateway.Server/MxGateway.Server.csproj
+```powershell
+dotnet build src/ZB.MOM.WW.MxGateway.Worker/ZB.MOM.WW.MxGateway.Worker.csproj -p:Platform=x86
 ```
 
 ## Related Documentation