Dates were rendered with the browser locale, ignoring the language chosen in
Personal settings, so a user browsing in German still saw US-style dates. All
date rendering now resolves its locale through a useDateLocale hook that returns
the selected language, augmented with the region from navigator.languages when
the language carries none (Intl reads a bare "en" as en-US). Applied to
DateField, the rated/loved tooltips, the mobile user list and album release
dates; the three inline timestamp tooltips now share a formatDateTime helper.
Closes#229
