Fix sent message editing interaction

[SuperstructureJH]

Summary

• edit sent text messages inline inside the original bubble, with Cancel and Send actions
• submit the edited prompt only after confirmation, then replace the visible conversation instead of leaving a second sidebar session
• preserve prior completed history, workspace, title, and agent preset; archive temporary revisions on failure

Supersedes #21, which was closed before this interaction correction.

Verification

• npm test
• npm run typecheck
• node --check node_modules/@deepseek-ai/dsh-client-ui-conversation/lib/client.js
• npm run package:mac:arm64
• packaged Electron UI acceptance: clicking Edit turns the original sent bubble into an inline editor; Cancel restores the message without changing the session