Fixes#938
The Defer Until field was using i18n.language directly instead of
resolveUserLocale(), causing it to display dates in MM/DD/YYYY format
(US default) regardless of timezone setting.
Now uses the same locale resolution pattern as the Due Date field,
which combines language with timezone-derived country code (e.g.,
"en" + Greek timezone → "en-GR" → DD/MM/YYYY format).
Changes:
- Import useMemo and resolveUserLocale
- Add displayLocale memo to resolve timezone-aware locale
- Use displayLocale instead of i18n.language in toLocaleString()
f1ea7843a7