Native <input type="date|time|datetime-local"> follows the browser
locale unless lang is set on the element itself — Chrome and Safari
ignore the document-root lang attribute for date-picker formatting.
initI18n and setLang now sweep every date/time/datetime-local input
and stamp the current locale, so DE users see dd.mm.yyyy and 24h on
every form (Termine, Fristen, Settings reminder times, Project
filing/grant dates, Fristenrechner trigger date, Appointments
filters). EN users keep their browser-locale defaults via lang="en".
The sweep runs on every page that calls initI18n (all of them) and
again on the DE/EN toggle, so live-switching language updates the
input formatting too. Inputs are static in the SSR templates today;
dynamically-injected date inputs would need an explicit re-sweep.
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