fix: pan board from empty space

src/App.tsx

@@ -518,7 +518,12 @@ function Board({ state, selected, linkFrom, recentlyCreatedExhibitId, recentlyCr
   const toggleFolder = (id: string) => update(s => ({ ...s, evidence: s.evidence.map(widget => widget.id === id ? { ...widget, config: { ...(widget.config || {}), open: !folderIsOpen(widget) } } : widget) }))
   const previewOrigin = linkFrom ? pointForId(linkFrom) : undefined
   return <div className={`board-viewport tool-${tool} ${linkFrom ? 'threading' : ''}`} ref={boardRef}
-    onPointerDown={e => { if (!(e.target as HTMLElement).closest('.thread-tag')) setExpandedThreadTagId(null); if (e.pointerType === 'touch' || tool === 'hand' || e.button === 1) { e.preventDefault(); pointerDown(e) } }}
+    onPointerDown={e => {
+      const target = e.target as HTMLElement
+      if (!target.closest('.thread-tag')) setExpandedThreadTagId(null)
+      const emptyBoardDrag = e.button === 0 && !target.closest('.evidence-card, .source-file-widget, .thread-tag, button')
+      if (e.pointerType === 'touch' || tool === 'hand' || e.button === 1 || emptyBoardDrag) { e.preventDefault(); pointerDown(e) }
+    }}
     onPointerMoveCapture={trackThreadPointer} onPointerMove={pointerMove} onPointerLeave={() => setThreadPointer(null)} onPointerUp={finishDrag} onPointerCancel={finishDrag} onAuxClick={e => { if (e.button === 1) e.preventDefault() }}>
     <div className="board" style={{ width: BOARD_W, height: BOARD_H, transform: `translate(${state.viewport.x}px, ${state.viewport.y}px) scale(${state.viewport.zoom})` }}>
       <div className="board-stamp">AUTHORIZED CITIZEN SCIENTIST WORKSTATION <span>GU-NET / 04</span></div>