fix: anchor board zoom to pointer

src/App.tsx

@@ -1,7 +1,7 @@
 import { useCallback, useEffect, useLayoutEffect, useMemo, useRef, useState } from 'react'
 import { BookOpen, Building2, CalendarClock, ChevronRight, CircleHelp, FileText, FolderOpen, Hand, Image as ImageIcon, Link2, Minus, MousePointer2, Network, NotebookPen, Pencil, Plus, RotateCcw, Search, Trash2, Upload, UserRound, X, ZoomIn, ZoomOut } from 'lucide-react'
 import type { BriefConcept, CaseDocument, CaseState, Connection, Evidence, LevelBrief, OrganizationKind, PartyKind, SourceFileType, TimelineRange, WidgetRelation } from './types'
-import { clampBoardZoom, containedIds, dateValue, folderIsOpen, moveBoardPoint, nextOpenBoardPosition, normalizeCase, panViewport, relationPosition, threadCurve, timelinePositionPercent, timelineRange, zoomFromPinch, zoomFromWheel } from './boardDomain'
+import { clampBoardZoom, containedIds, dateValue, folderIsOpen, moveBoardPoint, nextOpenBoardPosition, normalizeCase, panViewport, relationPosition, threadCurve, timelinePositionPercent, timelineRange, zoomFromPinch, zoomFromWheel, zoomViewportAt } from './boardDomain'
 import { documentWidget, exhibitWidget } from './exhibitRegistry'
 
 const BOARD_W = 2400
@@ -440,7 +440,9 @@ function Board({ state, selected, linkFrom, recentlyCreatedExhibitId, recentlyCr
       event.preventDefault()
       event.stopPropagation()
       if (event.ctrlKey || event.metaKey || event.deltaY === 0) return
-      update(s => ({ ...s, viewport: { ...s.viewport, zoom: zoomFromWheel(s.viewport.zoom, event.deltaY) } }))
+      const bounds = board.getBoundingClientRect()
+      const anchor = { x: event.clientX - bounds.left, y: event.clientY - bounds.top }
+      update(s => ({ ...s, viewport: zoomViewportAt(s.viewport, zoomFromWheel(s.viewport.zoom, event.deltaY), anchor) }))
     }
     board.addEventListener('wheel', handleWheelZoom, { passive: false })
     return () => board.removeEventListener('wheel', handleWheelZoom)
@@ -477,7 +479,11 @@ function Board({ state, selected, linkFrom, recentlyCreatedExhibitId, recentlyCr
         const points = [...touchPoints.current.values()]
         const distance = Math.hypot(points[1].x - points[0].x, points[1].y - points[0].y)
         const previous = pinchDistance.current
-        if (previous) update(s => ({ ...s, viewport: { ...s.viewport, zoom: zoomFromPinch(s.viewport.zoom, previous, distance) } }))
+        if (previous && boardRef.current) {
+          const bounds = boardRef.current.getBoundingClientRect()
+          const anchor = { x: (points[0].x + points[1].x) / 2 - bounds.left, y: (points[0].y + points[1].y) / 2 - bounds.top }
+          update(s => ({ ...s, viewport: zoomViewportAt(s.viewport, zoomFromPinch(s.viewport.zoom, previous, distance), anchor) }))
+        }
         pinchDistance.current = distance
         suppressClick.current = true
         event.preventDefault()