fix: remove redundant .to_dict() in list_tasks API

[lidaye910416]

Fix: Remove redundant .to_dict() in list_tasks API

Problem

The /api/graph/tasks endpoint throws AttributeError: 'dict' object has no attribute 'to_dict'.

Root Cause

TaskManager.list_tasks() already returns serialized dicts via .to_dict() at line 172 in task.py:

return [t.to_dict() for t in sorted(tasks, ...)]

But the API endpoint in graph.py:562 calls .to_dict() again on each item:

"data": [t.to_dict() for t in tasks],  # t is already a dict!

Fix

Simply return tasks directly since it is already a list of dicts.

Testing

• Before: curl /api/graph/tasks -> 500 Error
• After: curl /api/graph/tasks -> {"success": true, "data": [], "count": 0}