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);
     }
 }

backend/tests/PnvPanel.IntegrationTests/Activation/ActivationFlowTests.cs

@@ -56,7 +56,7 @@ public class ActivationFlowTests(PnvPanelWebApplicationFactory factory)
 
         var requestResponse = await userClient.PostJsonAsync(
             "/api/activation/request",
-            new { comment = (string?)null }
+            new { comment = "Erin, a friend of the admin" }
         );
         var request = await requestResponse.ReadAsAsync<ActivationRequestResponse>();
 
@@ -85,14 +85,29 @@ public class ActivationFlowTests(PnvPanelWebApplicationFactory factory)
 
         var first = await userClient.PostJsonAsync(
             "/api/activation/request",
-            new { comment = (string?)null }
+            new { comment = "Frank, a colleague of the admin" }
         );
         Assert.Equal(HttpStatusCode.OK, first.StatusCode);
 
         var second = await userClient.PostJsonAsync(
             "/api/activation/request",
-            new { comment = (string?)null }
+            new { comment = "Frank, a colleague of the admin" }
         );
         Assert.Equal(HttpStatusCode.Conflict, second.StatusCode);
     }
+
+    [Fact]
+    public async Task Request_WhenCommentEmpty_ReturnsBadRequest()
+    {
+        using var userClient = factory.CreateClient();
+        var userName = $"gina_{Guid.NewGuid():N}"[..20];
+        var (_, userToken) = await RegisterAndLoginAsync(userClient, userName, "P@ssw0rd123");
+        userClient.UseBearerToken(userToken);
+
+        var response = await userClient.PostJsonAsync(
+            "/api/activation/request",
+            new { comment = (string?)null }
+        );
+        Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
+    }
 }