[Bug]: Clarify acceptanceCriteria parameter format in task-creation guide

[lorenzb07]

Describe the bug
The task-creation guide returned by get_backlog_instructions(instruction="task-creation") describes acceptance criteria conceptually but doesn't specify the expected parameter format for task_create.

To Reproduce
Steps to reproduce the behavior:

1. Ask to the agent to create simple tasks from a plan
2. See error like: Error: Validation failed: Field 'acceptanceCriteria' must be an array

Expected behavior
No validation error on acceptance_criteria

[MrLesk]

Alex's Agent: This is already represented by PR #583. Leaving the issue open until that PR is reviewed and merged or replaced.