Suggestion: keep non-ASCII task JSON readable in s07_task_system.py

[f57y]

I noticed that task files in .tasks/task_*.json are currently saved with escaped Unicode sequences for non-ASCII text, which makes debugging harder when task subjects/descriptions contain Chinese.

Example:

• current: "\u6c47\u603b\u6210\u6700\u7ec8\u62a5\u544a"
• expected: "汇总成最终报告"

A small fix would be to use ensure_ascii=False in task-related json.dumps(...) calls.

If this sounds reasonable, I'd be happy to open a PR.