fix: terminal UTF-8 handling and UX

[shaw-baobao]

Summary

• ensure terminal sessions run with UTF-8 locale and decode output safely
• close the terminal panel when the last tab is closed
• tune xterm theme/background to avoid black flash and improve text contrast

Testing

• npm run lint
• npm run typecheck
• npm run test

[Dimillian]

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[Dimillian]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 3ac52645b4

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".