Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

…nth range headers

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

RAC's <CalendarMonthPicker> / <CalendarYearPicker> read `state.focusedDate.month`
for their displayed value. In a 2-month RangeCalendar, the focused date moves
when the user hovers a cell during an in-progress range pick (RAC's
`highlightDate` calls `setFocusedDate` to drive the highlight preview), so the
dropdown labels would jump even though the underlying grids stayed stable.

Pin the picker state Proxy's `focusedDate` to `state.visibleRange.start` (plus
the position offset) instead of `state.focusedDate`. This anchors the dropdown
labels to the GRID month and is no longer position-conditional — both left and
right pickers benefit from the stable label.

Adds a regression browser test.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

useCalendarState / useRangeCalendarState return plain object literals, so
{ ...baseState, focusedDate, setFocusedDate } gives the same result with no
trap mechanics. Drops useMemo too — RAC's state hook returns a fresh object
each render, so memoizing on baseState identity buys nothing.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

- Replace RACButton with antares Button (variant="minimal", size="sm")
  in CalendarHeader so prev/next inherit hover/focus/disabled styling
  from the design system. Drop the now-unused .navButton CSS.
- Trim verbose JSDoc on Calendar, RangeCalendar, and CalendarHeader.

…hevrons in RTL

- Rename internal `position?: 'single' | 'left' | 'right'` prop to
  `range?: 'start' | 'end'` (omit for single calendars). Names match the
  range value shape (`{ start, end }`) and are locale-direction-agnostic.
- Read `useLocale()` and flip the prev/next chevron icons in RTL so they
  point opposite the reading direction (matches RAC's recommended pattern).
- Update the calendar.node SSR snapshot — the prior Button-swap commit's
  markup change (.navButton → antares Button classes) was never captured.