The issue and project start/due-date pickers were near-complete copies of the
same Popover + Calendar + clear wiring, so they could drift in behaviour or
formatting. Extract that into one entity-agnostic DateOnlyPicker
(packages/views/common/date-only-picker.tsx); each of the four pills is now a
thin wrapper supplying only its field name (via onChange), icon, overdue flag,
and localized copy. -264 lines of duplication, single source of truth.
Behaviour is unchanged: the issue pickers keep their full API (trigger /
triggerRender / open / onOpenChange / align / defaultOpen — all still used by
board-card, issue-detail, create-issue) and the calendar-day contract stays in
@multica/core/issues/date. The en-US display format now lives in one place
rather than being duplicated per entity.
Full views test suite (1857 tests) + typecheck + lint pass.
Part of #5227
Co-authored-by: multica-agent <github@multica.ai>