fix: preserve Claude terminal outcomes

[bytehello]

Summary

Fixes #292.

The Claude backend now maps ResultMessage terminal signals onto the existing normalized turn states instead of hardcoding every result to completed:

• aborted streaming or tool execution becomes interrupted
• max-turn, API, and other error results become failed with an actionable error
• successful results remain unchanged

This keeps the fix at the translator seam already shared by interactive and autonomous turns.

Validation

• tests/test_engine.py: 91 passed
• Python compile check passed
• Full suite: 3380 passed; 6 existing MemU date tests failed under Asia/Shanghai because a timezone conversion produced the prior UTC date
• The same MemU date group passes under UTC: 11 passed

No engine or persistence changes were needed.

[CLAassistant]

All committers have signed the CLA.

[alex-clickhouse]

LGTM, thank you for the PR!