Default AI content language to Ukrainian

[axies20]

What changed

• add Ukrainian (uk) as a supported AI content language
• make Ukrainian the default for newly created workspaces
• default the workspace creation form and empty settings fallback to Ukrainian
• keep UI locale support independent from AI content languages
• cover the new enum option, default, prompt language, workspace creation, and locale relationship with Pest tests

Why

AI content generation previously defaulted to English and Ukrainian was not available in the workspace content-language list. This makes Ukrainian the default without silently overwriting the language selected by existing workspaces.

Validation

• git diff --check passes
• npm ci succeeds
• npm run build was attempted, but Wayfinder cannot run because PHP is not available in the environment PATH
• Pint and Pest could not run for the same missing-PHP environment limitation