feat(grid): auto-scroll while dragging cell selection

apps/desktop/src/components/grid/DataGrid.vue

@@ -4599,6 +4599,8 @@ const selection = useDataGridSelection({
   showTranspose,
   transposeRowIndex,
   gridRef,
+  getScrollElement: dataGridSelectionScroller,
+  cellFromClientPoint: dataGridCellFromClientPoint,
 });
 
 const {
@@ -5616,6 +5618,35 @@ function canvasScrollerElement(): HTMLElement | null {
   return null;
 }
 
+function dataGridSelectionScroller(): HTMLElement | null {
+  if (showTranspose.value) return null;
+  return canvasScrollerElement();
+}
+
+function dataGridCellFromClientPoint(clientX: number, clientY: number): { rowIndex: number; colIndex: number } | null {
+  const scroller = dataGridSelectionScroller();
+  if (!scroller) return null;
+  const rect = scroller.getBoundingClientRect();
+  const clampedX = Math.min(rect.right - 1, Math.max(rect.left + DATA_GRID_ROW_NUM_WIDTH + 1, clientX));
+  const clampedY = Math.min(rect.bottom - 1, Math.max(rect.top + 1, clientY));
+
+  if (useCanvasGridRows.value) {
+    const rowIndex = Math.floor((scroller.scrollTop + clampedY - rect.top) / CANVAS_DATA_GRID_ROW_HEIGHT);
+    const visibleColIdx = canvasColumnAt(scroller.scrollLeft + clampedX - rect.left - DATA_GRID_ROW_NUM_WIDTH);
+    if (rowIndex < 0 || rowIndex >= displayRowCount.value || visibleColIdx < 0) return null;
+    const item = displayItemAt(rowIndex);
+    return item ? { rowIndex: item.displayIndex, colIndex: visibleColIdx } : null;
+  }
+
+  const target = document.elementFromPoint(clampedX, clampedY);
+  const cell = target instanceof Element ? target.closest<HTMLElement>("[data-row-index] [data-visible-col-index]") : null;
+  const row = cell?.closest<HTMLElement>("[data-row-index]");
+  const rowIndex = Number(row?.dataset.rowIndex);
+  const colIndex = Number(cell?.dataset.visibleColIndex);
+  if (!Number.isInteger(rowIndex) || !Number.isInteger(colIndex)) return null;
+  return { rowIndex, colIndex };
+}
+
 function syncCanvasViewport() {
   if (!dataGridIsActive) return;
   const scroller = canvasScrollerElement();