fix: separate desktop wheel and mobile pinch zoom

src/boardDomain.test.ts

@@ -14,6 +14,7 @@ import {
   timelinePositionPercent,
   timelineRange,
   zoomFromWheel,
+  zoomFromPinch,
 } from './boardDomain'
 
 const folder: Evidence = {
@@ -53,11 +54,15 @@ describe('board coordinate math', () => {
     expect(panViewport(state.viewport, { x: 25, y: -10 })).toEqual({ x: 35, y: 10, zoom: 0.5 })
   })
 
-  it('clamps toolbar and pinch zoom to the same limits', () => {
+  it('clamps toolbar, wheel, and touch pinch zoom to the same limits', () => {
     expect(clampBoardZoom(-10)).toBe(MIN_BOARD_ZOOM)
     expect(clampBoardZoom(10)).toBe(MAX_BOARD_ZOOM)
     expect(zoomFromWheel(1, 10_000)).toBe(MIN_BOARD_ZOOM)
     expect(zoomFromWheel(1, -10_000)).toBe(MAX_BOARD_ZOOM)
+    expect(zoomFromWheel(1, 100)).toBeCloseTo(0.85)
+    expect(zoomFromPinch(1, 100, 125)).toBeCloseTo(1.25)
+    expect(zoomFromPinch(1, 100, 50)).toBeCloseTo(0.5)
+    expect(zoomFromPinch(1, 0, 120)).toBe(1)
   })
 
   it('places new exhibits in deterministic open slots', () => {