Date fields in the task edit page used i18n.language (e.g. "en") to
determine date format, giving MM/DD for English even when the user's
timezone indicates a DD/MM region (e.g. Europe/Athens).
Enhance resolveUserLocale to derive the country from the user's
timezone and combine it with the language (e.g. "en" + "GR" = "en-GR")
so date formatting follows regional conventions.
