Codex/vietnamese UI ci fixes

[khanhdeptraivaicachuong]

No description provided.

[BigPizzaV3]

Thanks for the contribution. I don't think this PR is ready to merge in its current form.

The main issue is that it does more than add Vietnamese UI support: several existing default strings and install names are changed globally, so Chinese/English users would also see Vietnamese or renamed entries.

Please adjust the PR to keep it scoped to Vietnamese i18n:

• Do not hard-code Vietnamese strings in assets/inject/renderer-inject.js. The injected Codex++ menu should keep the existing language behavior, or localization should be driven by the selected language setting.
• Do not replace source/default UI text directly, e.g. apps/codex-plus-manager/src/model-windows.ts currently returns a Vietnamese error message for every user.
• Remove generated/backup files that should not be committed, especially apps/codex-plus-manager/src/i18n.ts.bak.
• Avoid changing installer/app/shortcut names from Codex++ 管理工具 to Codex++ Manager in this PR. If that change is needed for packaging or CI, it should be a separate PR with its own rationale.
• Please make sure CI/checks run successfully after the cleanup.

A good shape for this PR would be: add i18n-vi.ts, extend the language selector to include Vietnamese, and keep all existing Chinese/English/default behavior unchanged unless the selected language is Vietnamese.