fix(02): fix week/day time-grid clip and hour-label contrast

- CalendarShell: remove overflow:hidden from calendar container; add
  height:100% so Schedule-X .sx__calendar-wrapper can fill the flex
  parent and .sx__view-container can scroll.
- index.css: add explicit .sx__calendar-wrapper { height: 100% } rule
  to propagate height through the React adapter's wrapper element.
- tokens.css: fix --sx-color-neutral override from near-white
  var(--color-surface-dim) to readable var(--color-text-secondary);
  fix --sx-color-neutral-variant to var(--color-border); add
  --sx-internal-color-text override for chevrons and UI borders.
  Both hour-axis labels (.sx__week-grid__hour-text) and weekday/day
  name headers (.sx__week-grid__day-name, .sx__week-grid__date-number)
  use --sx-color-neutral — all now readable.

Class and variable names confirmed from @schedule-x/theme-default@4.6.0
dist/index.css inspection.

apps/pwa/src/components/CalendarShell.tsx

@@ -205,7 +205,7 @@ export function CalendarShell() {
         }}
       >
         {/* Main calendar area */}
-        <div style={{ flex: 1, minHeight: 0, position: 'relative', overflow: 'hidden' }}>
+        <div style={{ flex: 1, minHeight: 0, height: '100%', position: 'relative' }}>
           {isInitialLoading ? (
             // Loading state: shimmer skeleton
             <div style={{ padding: 'var(--space-4)', flex: 1 }}>