Initial commit: base slice (auth, roles, users, admin) scaffold

Backend: .NET 10 Clean Architecture + LiteCqrs.Net + EF Core/PostgreSQL +
Identity/JWT. Frontend: React 19 + Vite + TanStack Query/Router + Tailwind v4
with a retro CRT theme. Docker/compose deployment mirroring PnvPanel's
conventions, scoped down to the current base feature set.

backend/src/TeleWave.Application/Auth/ChangeUserName/ChangeUserNameCommandValidator.cs

@@ -0,0 +1,11 @@
+using FluentValidation;
+
+namespace TeleWave.Application.Auth.ChangeUserName;
+
+public sealed class ChangeUserNameCommandValidator : AbstractValidator<ChangeUserNameCommand>
+{
+    public ChangeUserNameCommandValidator()
+    {
+        RuleFor(x => x.NewUserName).NotEmpty().MinimumLength(3).MaximumLength(64);
+    }
+}