fix(gantt): preserve horizontal scroll when focusing a task bar

Focusing the task bar SVG `<g role="slider">` inside the
`overflow-x:auto` `.gantt-container` triggered Firefox's focus-induced
scroll-into-view, which jumped the scroll container back toward
`scrollLeft=0` (today). Pass `{ preventScroll: true }` to `focus()` so
selecting a bar keeps the current scroll position. Chromium scrolls
minimally on focus so it never manifested there.

Fixes #2728

frontend/src/components/gantt/GanttChart.vue

@@ -730,7 +730,7 @@ function focusTaskBar(rowId: string) {
 	setTimeout(() => {
 		const taskBarElement = document.querySelector(`[data-row-id="${rowId}"] [role="slider"]`) as HTMLElement
 		if (taskBarElement) {
-			taskBarElement.focus()
+			taskBarElement.focus({preventScroll: true})
 		}
 	}, 0)
 }