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.

tasks.go

@@ -41,7 +41,7 @@ func (c *Client) GetAllTasks(ctx context.Context, projectID int, status TaskStat
 
 // CreateTask creates a new task and returns the created task.
 func (c *Client) CreateTask(ctx context.Context, req CreateTaskRequest) (*Task, error) {
-	var taskID int
+	var taskID IntOrFalse
 	if err := c.call(ctx, "createTask", req, &taskID); err != nil {
 		return nil, fmt.Errorf("createTask: %w", err)
 	}
@@ -51,7 +51,7 @@ func (c *Client) CreateTask(ctx context.Context, req CreateTaskRequest) (*Task,
 	}
 
 	// Fetch the created task to return full details
-	return c.GetTask(ctx, taskID)
+	return c.GetTask(ctx, int(taskID))
 }
 
 // UpdateTask updates an existing task.