Add Vietnamese (vi) locale to UI and language selector

[huytu250]

Summary\n- Adds Vietnamese (vi) locale support to the UI.\n\nChanges\n- Add 'vi' to default language lists in desktop and prod configs.\n- Introduce ui.string.Vietnamese and wire it into SettingsPopup.\n- Update SettingsPopup to include 'vi' option and appropriate flag.\n- Provide packages/ui/lang/vi.json with complete translations based on en.json.\n\nBehavior\n- Language picker now shows 'Tiếng Việt'.\n- UI strings render in Vietnamese where available; per-key fallback remains English as designed.\n\nVerification\n- Ran webpack dev server locally and verified language selection and core UI strings on http://localhost:8080/.\n- No build errors observed.\n\nNotes\n- Other packages (outside UI) continue to fall back to English until their vi.json files are added.\n- No breaking changes; metadata Languages updated to include 'vi'.

[huly-github-staging[bot]]

Connected to Huly®: UBERF-13955

[ArtyomSavchenko]

Hi @huytu250 Could you please sign your commit? For example, the following command can be used to sign the latest commit: git commit -s --amend This will allow our CI to be completed successfully