Add IntOrFalse type to handle polymorphic API responses

Kanboard API returns int (ID) on success and false (bool) on failure
for create operations. Add IntOrFalse type that handles both cases
and update CreateTask, CreateComment, CreateTag, CreateTaskFile, and
CreateTaskLink to use it.

comments.go

@@ -42,7 +42,7 @@ func (c *Client) CreateComment(ctx context.Context, taskID, userID int, content
 		"content": content,
 	}
 
-	var commentID int
+	var commentID IntOrFalse
 	if err := c.call(ctx, "createComment", params, &commentID); err != nil {
 		return nil, fmt.Errorf("createComment: %w", err)
 	}
@@ -52,7 +52,7 @@ func (c *Client) CreateComment(ctx context.Context, taskID, userID int, content
 	}
 
 	// Fetch the created comment to return full details
-	return c.GetComment(ctx, commentID)
+	return c.GetComment(ctx, int(commentID))
 }
 
 // UpdateComment updates the content of a comment.