[codex] 增加安全起草模式

[xiaojin5222-ui]

Summary

• add a safe draft mode that fills the chat input without sending and keep auto-send available as an explicit mode
• split device actions into draft-fill and send paths, and branch session behavior on replyMode
• add a minimal session behavior harness plus update the home UI and copy for mode switching and draft logs

Why

• the previous default behavior auto-sent replies immediately after generation, which was too risky for day-to-day use
• this change makes the safer human-in-the-loop flow the default while preserving the existing automation path for explicit use

Validation

• npm run test:session
• npm run typecheck
• npm run build