feat: scaleY pinch-to-zoom with counter-scaling and zoomScale persistence

[anton-patrushev]

Summary

• Rewrites pinch-to-zoom to use GPU-accelerated transform: [{ scaleY: zoomScale }] — timeIntervalHeight stays constant, only zoomScale changes per frame
• Counter-scales hour labels, now indicator, event text, drag dots, horizontal grid lines, and draggable/dragging event components
• Fixes onZoomChange to clamp zoomScale before computing zoomPercent, preventing spring overshoot from reporting out-of-range values
• Adds initialZoomScale prop for consumer-provided initial zoom, minZoomScale/maxZoomScale on context
• Exposes counterScaleStyle via BodyContext for shared counter-scale animated style

Architecture

ScrollView
  └─ Animated.View { height: timelineHeight * zoomScale }     ← scroll spacer
      └─ Animated.View { height: timelineHeight,               ← GPU scaling
                         transform: [{ scaleY: zoomScale }],
                         transformOrigin: '0% 0%' }
            └─ content (TimeColumn, Grid, Events, NowIndicator, Drag overlay)

Performance model

• During pinch: 1 SharedValue write (zoomScale) + 1 outer spacer height update. GPU handles visual scaling. No content re-layout.
• Before: timeIntervalHeight changes → minuteHeight derives → timelineHeight derives → ALL event heights derive → full layout recalc

Stacked on

• fix/remove-header-bottom-border

Test plan

• Pinch gesture: zoom in/out, focal point stays stable, no scroll jumping
• Counter-scaling: hour labels, now indicator, event text all remain unwarped
• Drag to create/edit: correct time snapping at all zoom levels
• Tap on background: correct time reported at all zoom levels
• goToHour(), goToDate(), zoom() work at all zoom levels
• Overscroll spring: rubber-band feel at min/max bounds
• Web ctrl+wheel: zoom works on web

🤖 Generated with Claude Code