fix(client-controller): single constructor with IHtmlLocalizer

The partial class ClientController had two constructors declared
across ClientController.cs and ClientController.Collections.cs.
ASP.NET Core DI failed to pick one at request time with:

  System.InvalidOperationException: Multiple constructors accepting
  all given argument types have been found in type
  'Yavsc.Controllers.ClientController'.

Move IHtmlLocalizer<ClientController> into the primary constructor
in ClientController.cs and drop the duplicate one in
ClientController.Collections.cs. The Collections partial now keeps
only its readonly field and action methods; the constructor and
field assignment are unified on the main file.

Also add the missing 'using Microsoft.AspNetCore.Mvc.Localization;'
to ClientController.cs so IHtmlLocalizer resolves.

.gitignore

@@ -27,3 +27,6 @@ appsettings-*.*.json
 generated/
 *.tmp
 DataDir/
+
+*.tests.trx
+*.tests.html