i18n: add Russian and Ukrainian translations for new UI strings - #29601

Relates to #2790

Checklist

• This PR targets the dev branch.
• This PR links to a well-described, confirmed Issue or active Discussion: Closes #___ / Relates to #___.
• A maintainer explicitly asked me to open this PR, or this PR only updates i18n/localization.
• The change is one logical unit with no unrelated commits.
• I matched nearby code patterns and avoided unnecessary new settings, abstractions, or dependencies.
• I manually tested the changed workflow and any nearby behavior that could be affected.
• I updated relevant docs, including the Open WebUI Docs Repository, if needed.
• I added screenshots for UI changes, and a recording when motion or interaction matters.
• I reviewed any AI-generated code before submitting it.
• The PR title uses one of the prefixes listed below.

Summary

Adds translations for all 77 newly introduced UI strings in both the Russian and Ukrainian locale files.

The translations follow terminology already used throughout each locale and were reviewed in their UI contexts. Russian and Ukrainian were checked separately to ensure natural grammar and prevent Russian vocabulary from appearing in the Ukrainian translations.

Testing

• Confirmed both locale files contain no empty translation values.
• Confirmed their key sets match dev.
• Confirmed all interpolation placeholders are preserved.
• Successfully parsed both files as JSON.
• Successfully ran Prettier against both files.
• Reviewed commonly visible UI terminology against existing translations.
• Audited Ukrainian additions for Russian-specific letters and terminology.
• Confirmed the commit changes only:
  • src/lib/i18n/locales/ru-RU/translation.json
  • src/lib/i18n/locales/uk-UA/translation.json

Contributor License Agreement

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