fix(gantt): ensure chart container fills viewport width for narrow date ranges

Adds min-inline-size: 100% to .gantt-container so the scrollable area
never appears narrower than the card width, even with short date ranges.

Ref #2337

frontend/src/components/gantt/GanttChart.vue

@@ -751,6 +751,7 @@ onUnmounted(() => {
 <style scoped lang="scss">
 .gantt-container {
 	overflow-x: auto;
+	min-inline-size: 100%;
 }
 
 .gantt-chart-wrapper {