Implement activation checks across various commands and queries

- Introduced `IRequiresActivation` interface to enforce activation requirements for multiple commands and queries, ensuring that only activated users can create, edit, or access configurations, news, and applications.
- Updated the `RequireActivationBehavior` to handle activation checks uniformly, returning appropriate errors for unauthenticated or inactive users.
- Enhanced error handling by adding `NotActivated` error to provide clear feedback for users attempting to access restricted features.
- Updated documentation to reflect the new activation requirements and their implications on user access and functionality.

backend/src/PnvPanel.Application/Auth/AuthErrors.cs

@@ -21,4 +21,7 @@ public static class AuthErrors
 
     public static readonly Error UserBlocked =
         Error.Forbidden("Auth.UserBlocked", "Аккаунт заблокирован администратором.");
+
+    public static readonly Error NotActivated =
+        Error.Forbidden("Auth.NotActivated", "Аккаунт не активирован — обратитесь к администратору.");
 }