fix(galaxy): complete PR 7.2 rename — use canonical GalaxyMxGateway driver type

The driver/factory/seed use 'GalaxyMxGateway' (legacy 'Galaxy' was retired),
but the AdminUI editor router, GalaxyDriverPage, address picker, identity
dropdown, the Galaxy browser/probe, and DraftValidator still keyed on 'Galaxy'.
Result: the seeded GalaxyMxGateway driver couldn't be edited ('no editor
registered'), UI-created Galaxy drivers wrote a type with no factory, and a
SystemPlatform-bound GalaxyMxGateway driver failed publish validation.
Align all stragglers to GalaxyMxGateway (+ failing-test-first DraftValidator
coverage). ShouldStub's 'Galaxy' legacy safety-net left intact.

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Browser.Tests/GalaxyDriverBrowserTests.cs

@@ -16,10 +16,10 @@ public sealed class GalaxyDriverBrowserTests
 {
     private readonly GalaxyDriverBrowser _sut = new();
 
-    /// <summary>The DriverType key must match the AdminUI's persisted "Galaxy" value
+    /// <summary>The DriverType key must match the AdminUI's persisted "GalaxyMxGateway" value
     /// so the factory wire-up picks the right browser implementation.</summary>
     [Fact]
-    public void DriverType_is_Galaxy() => _sut.DriverType.ShouldBe("Galaxy");
+    public void DriverType_is_GalaxyMxGateway() => _sut.DriverType.ShouldBe("GalaxyMxGateway");
 
     /// <summary>An empty Gateway.Endpoint must fail fast with a clear, endpoint-mentioning
     /// message rather than surfacing a downstream gRPC URI parse error.</summary>