fix(wechat): check abort flag in streaming loop to honor /stop command

[Kailigithub]

Problem

Closes #396

In WeChat clawbot mode, when a user sends /stop during task execution, the _task_aborted flag is set but _handle() never checks it inside its streaming loop. The loop blocks on dq.get(timeout=300) and continues processing accumulated intermediate results, sending them to the user before finally showing [任务已完成].

Root Cause

The while True loop in _handle() (line 373) only breaks on 'done' in item or queue.Empty timeout. It never checks _task_aborted[uid], so the abort flag is only evaluated after the loop exits — by which time all accumulated results have already been sent.

Fix

Added an abort check at the top of each loop iteration:

if _task_aborted.get(uid): break

Also changed dq.get(timeout=300) to use a try/except for queue.Empty so the abort check runs every 300s instead of blocking indefinitely. This ensures the /stop command takes effect within one queue poll cycle.

Verification

• python3 -m py_compile frontends/wechatapp.py — no syntax errors
• ruff check frontends/wechatapp.py — no new issues introduced