Enhance activation request validation and documentation

- Updated the `RequestActivationCommandValidator` to require a non-empty comment, ensuring that users provide necessary identification information.
- Modified integration tests to validate the new requirement for a comment, including a test for handling empty comments.
- Updated API documentation to reflect that the comment is now mandatory and clarified its purpose.
- Enhanced frontend components to enforce comment requirements and provide user guidance on the comment's importance.

backend/src/PnvPanel.Application/Activation/RequestActivationCommandValidator.cs

@@ -6,6 +6,7 @@ public sealed class RequestActivationCommandValidator : AbstractValidator<Reques
 {
     public RequestActivationCommandValidator()
     {
-        RuleFor(x => x.Comment).MaximumLength(500);
+        // Комментарий обязателен: по нему админ понимает, кто заявитель и откуда.
+        RuleFor(x => x.Comment).NotEmpty().MaximumLength(500);
     }
 }