add Vietnamese (vi) locale

[0jar]

Initial translations for Vietnamese (vi)

• Claimed language: filed issue Contribution | Translation: Vietnamese (vi) #231
• Locale JSON: frontend/src/lib/i18n/locales/vi.json created with all ~900+ keys translated, including the extension keys in frontend/src/lib/i18n/locales/en.json
• Register locale: added register() call in frontend/src/lib/i18n/index.ts
• Supported locales: added entry to supportedLocales array in the same file
• date-fns locale: added case in frontend/src/lib/i18n/dateFnsLocale.ts
• AppStream metainfo: added xml:lang="vi" entries in build/flatpak/io.github.hkdb.Aerion.metainfo.xml
• Desktop entry: added [vi] suffixed keys in build/linux/aerion.desktop
• Checks pass: npm run check, npm run build, and go test ./... all pass
• Live tested: app launched with make dev, language switched, all strings verified
• Detached composer: composer window also displays the correct language

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Issues found

1. The settings bar is a little tightly packed for Vietnamese:

2. Also, the Contacts plugin details hasn't been translated yet, I assume this is in /extensions/contacts/frontend/i18n/locales/en.json instead of the global file. Do I translate that too?

[hkdb]

Sorry for the late follow-up. Please hang tight. I am in the middle of implementing the extension system with Calendar and Contacts that will yield further translation requirements. Would love to see if you can sync and translate those too all at once. I am guessing I will need another week at most to get to working with you on this PR. Will keep you posted. Thanks!

PS. For the settings tabs, any way we can be creative to use shorter variations to ensure they look right? Meanwhile, I will look into auto-adjusting based on label length.

[0jar]

Yep, no worries, I'll wait to sync the extension work too. No need to rush :3

For the settings tabs, yeah we can do shorter variations for now. I can trim "Trình soạn thảo" to "Trình soạn" and "Tiện ích mở rộng" to "Tiện ích" and they'd still be clear.