fix(cron): handle CancelledError so cancelled jobs report correct status

[mvanhorn]

Summary

When a cron job's asyncio task is cancelled (shutdown, timeout, manual cancellation), asyncio.CancelledError is raised. Since Python 3.8, CancelledError inherits from BaseException - not Exception - so the existing except Exception blocks in the cron module silently miss it. The result: cancelled jobs report "running" (or a stale "success" from the prior run) instead of reflecting the cancellation.

Fix: Add explicit except asyncio.CancelledError handlers before every except Exception in:

• CronManager._execute_once() - sets last_status = "cancelled" and re-raises
• CronManager._heartbeat_callback() - logs and re-raises
• CronExecutor.execute() - catches both TimeoutError and CancelledError, logs, and re-raises

Also adds "cancelled" to the CronJobState.last_status Literal type in models.py.

This follows the established pattern in app/runner/runner.py:274 and app/channels/dingtalk/channel.py:1559 which already handle CancelledError explicitly.

Changes

• src/copaw/app/crons/manager.py: Add except asyncio.CancelledError in _execute_once() and _heartbeat_callback()
• src/copaw/app/crons/executor.py: Add except asyncio.TimeoutError and except asyncio.CancelledError around wait_for() call
• src/copaw/app/crons/models.py: Add "cancelled" to CronJobState.last_status Literal

Test plan

• ruff check passes
• Cancel a running cron task and verify last_status == "cancelled" instead of "success" or "running"
• Timeout a cron job and verify the timeout is logged before the error propagates

Closes #1829

This contribution was developed with AI assistance (Claude Code + Codex).

[xieyxclack]

LGTM. Thank you for your contribution!

[mvanhorn]

Thanks for the review and merge.