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.

docs/api-design.md

@@ -146,7 +146,7 @@ status, createdAt }`. `expiresAt` всегда `null` (лимиты по сро
 | Метод | Путь                        | Роль | Тело запроса     | Тело ответа                                            |
 | ----- | --------------------------- | ---- | ----------------- | -------------------------------------------------------- |
 | GET   | `/api/activation/status`    | user | —                  | `{ isActivated, pendingRequest: { id, comment, createdAt } \| null }` |
-| POST  | `/api/activation/request`   | user | `{ comment? }`     | `{ id, comment, createdAt }`                              |
+| POST  | `/api/activation/request`   | user | `{ comment }` (обязателен, ≤500) | `{ id, comment, createdAt }`                              |
 
 ## Billing (пользователь)