fix(gantt): improve parent task bar styling and visual grouping

- Make parent task bars full height (32px) matching regular bars,
  instead of the thin 8px summary bar
- Move collapse/expand chevron to sit right before the bar start
  position so it moves with the task during drag/resize
- Remove fixed-position indent indicator lines
- Add light background band with rounded border to visually group
  parent tasks with their children, sized to fit the bars

frontend/src/components/gantt/GanttChart.vue

@@ -32,6 +32,18 @@
 			>
 				<template #default="{ focusedRow, focusedCell }">
 					<div class="gantt-rows-container">
+						<!-- Group background bands for parent-child visual grouping -->
+						<div
+							v-for="(band, bandIndex) in parentGroupBands"
+							:key="`band-${bandIndex}`"
+							class="gantt-group-band"
+							:style="{
+								top: `${band.startIndex * ROW_HEIGHT}px`,
+								height: `${(band.endIndex - band.startIndex + 1) * ROW_HEIGHT}px`,
+								left: `${band.left}px`,
+								width: `${band.width}px`,
+							}"
+						/>
 						<div class="gantt-rows">
 							<GanttRow
 								v-for="(rowId, index) in ganttRows"
@@ -52,7 +64,6 @@
 										:focused-row="focusedRow ?? null"
 										:focused-cell="focusedCell"
 										:row-id="rowId"
-										:indent-level="ganttBars[index]?.[0]?.meta?.indentLevel ?? 0"
 										:is-parent="ganttBars[index]?.[0]?.meta?.isParent ?? false"
 										:is-collapsed="collapsedTaskIds.has(Number(ganttBars[index]?.[0]?.id))"
 										@barPointerDown="handleBarPointerDown"
@@ -393,6 +404,57 @@ const relationArrows = computed<GanttArrow[]>(() => {
 
 const totalHeight = computed(() => ganttRows.value.length * ROW_HEIGHT)
 
+// Compute parent-child group bands for visual grouping background
+const GROUP_BAND_PADDING = 12
+
+const parentGroupBands = computed(() => {
+	const bands: Array<{ startIndex: number; endIndex: number; left: number; width: number }> = []
+	const bars = ganttBars.value
+	const positions = barPositions.value
+
+	for (let i = 0; i < bars.length; i++) {
+		const bar = bars[i]?.[0]
+		if (!bar?.meta?.isParent) continue
+
+		const parentLevel = bar.meta.indentLevel ?? 0
+		let endIndex = i
+
+		// Find last consecutive child with deeper indent
+		for (let j = i + 1; j < bars.length; j++) {
+			const childBar = bars[j]?.[0]
+			const childLevel = childBar?.meta?.indentLevel ?? 0
+			if (childLevel <= parentLevel) break
+			endIndex = j
+		}
+
+		// Only create a band if there are actual children visible
+		if (endIndex > i) {
+			// Compute horizontal extent from bar positions
+			let minX = Infinity
+			let maxX = -Infinity
+
+			for (let k = i; k <= endIndex; k++) {
+				const taskId = Number(bars[k]?.[0]?.id)
+				const pos = positions.get(taskId)
+				if (!pos) continue
+				minX = Math.min(minX, pos.x)
+				maxX = Math.max(maxX, pos.x + pos.width)
+			}
+
+			if (minX < Infinity) {
+				bands.push({
+					startIndex: i,
+					endIndex,
+					left: minX - GROUP_BAND_PADDING,
+					width: maxX - minX + GROUP_BAND_PADDING * 2,
+				})
+			}
+		}
+	}
+
+	return bands
+})
+
 function updateGanttTask(id: string, newStart: Date, newEnd: Date) {
 	const task = tasks.value.get(Number(id))
 	if (!task) return
@@ -701,6 +763,15 @@ onUnmounted(() => {
 	position: relative;
 }
 
+.gantt-group-band {
+	position: absolute;
+	background: hsla(var(--primary-h), var(--primary-s), var(--primary-l), 0.06);
+	border: 1px solid hsla(var(--primary-h), var(--primary-s), var(--primary-l), 0.12);
+	border-radius: 6px;
+	pointer-events: none;
+	z-index: 1;
+}
+
 .gantt-rows {
 	position: relative;
 	z-index: 2;

frontend/src/components/gantt/GanttRowBars.vue

@@ -8,24 +8,11 @@
 		:aria-label="$t('project.gantt.taskBarsForRow', { rowId })"
 		:data-row-id="rowId"
 	>
-		<!-- Indent indicator: thin vertical lines for nesting depth -->
-		<line
-			v-for="level in indentLevel"
-			:key="`indent-${level}`"
-			:x1="(level - 1) * 16 + 8"
-			:y1="0"
-			:x2="(level - 1) * 16 + 8"
-			:y2="40"
-			stroke="var(--grey-300)"
-			stroke-width="1"
-			class="gantt-indent-line"
-		/>
-
-		<!-- Collapse/expand chevron for parent tasks -->
+		<!-- Collapse/expand chevron for parent tasks — positioned just before the bar -->
 		<g
-			v-if="isParent"
+			v-if="isParent && bars[0]"
 			class="gantt-collapse-toggle"
-			:transform="`translate(${indentLevel * 16 + 2}, 12)`"
+			:transform="`translate(${getBarX(bars[0]) - 18}, 12)`"
 			role="button"
 			:aria-label="isCollapsed
 				? $t('project.gantt.expandGroup', { task: bars[0]?.meta?.label || '' })
@@ -117,7 +104,7 @@
 				@pointerdown="handleBarPointerDown(bar, $event)"
 			/>
 
-			<!-- Parent summary bar (thinner with diamond endpoints) -->
+			<!-- Parent summary bar (full height with diamond endpoints) -->
 			<g
 				v-if="bar.meta?.isParent"
 				class="gantt-bar gantt-parent-bar"
@@ -126,12 +113,12 @@
 				:aria-pressed="isRowFocused"
 				@pointerdown="handleBarPointerDown(bar, $event)"
 			>
-				<!-- Thin horizontal bar -->
 				<rect
-					:x="getBarX(bar) + 6"
-					:y="16"
-					:width="Math.max(0, getBarWidth(bar) - 12)"
-					:height="8"
+					:x="getBarX(bar)"
+					:y="4"
+					:width="getBarWidth(bar)"
+					:height="32"
+					:rx="4"
 					:fill="getBarFillAttr(bar)"
 					:opacity="bar.meta?.isDone ? 0.5 : 1"
 					:stroke="getBarStroke(bar)"
@@ -141,18 +128,14 @@
 				<!-- Left diamond -->
 				<polygon
 					:points="getLeftDiamondPoints(bar)"
-					:fill="getBarFillAttr(bar)"
+					:fill="getParentDiamondFill(bar)"
 					:opacity="bar.meta?.isDone ? 0.5 : 1"
-					:stroke="getBarStroke(bar)"
-					:stroke-width="getBarStrokeWidth(bar)"
 				/>
 				<!-- Right diamond -->
 				<polygon
 					:points="getRightDiamondPoints(bar)"
-					:fill="getBarFillAttr(bar)"
+					:fill="getParentDiamondFill(bar)"
 					:opacity="bar.meta?.isDone ? 0.5 : 1"
-					:stroke="getBarStroke(bar)"
-					:stroke-width="getBarStrokeWidth(bar)"
 				/>
 			</g>
 
@@ -249,7 +232,6 @@ const props = defineProps<{
 	focusedRow: string | null
 	focusedCell: number | null
 	rowId: string
-	indentLevel: number
 	isParent: boolean
 	isCollapsed: boolean
 }>()
@@ -334,17 +316,15 @@ const getBarTextX = computed(() => (bar: GanttBarModel) => {
 	}
 	// When the bar starts before the visible range, clamp text to the left edge
 	// so the title remains visible within the visible portion of the bar.
-	// For parent bars, offset by the chevron width
-	const baseOffset = bar.meta?.isParent ? 24 : 8
-	return Math.max(getBarX.value(bar) + baseOffset, 8)
+	return Math.max(getBarX.value(bar) + 8, 8)
 })
 
 // Diamond endpoint helpers for parent summary bars
-const DIAMOND_SIZE = 6
+const DIAMOND_SIZE = 5
 
 function getLeftDiamondPoints(bar: GanttBarModel): string {
 	const x = getBarX.value(bar)
-	const cy = 20 // vertical center of the thin bar
+	const cy = 20 // vertical center of the bar
 	return `${x},${cy} ${x + DIAMOND_SIZE},${cy - DIAMOND_SIZE} ${x + DIAMOND_SIZE * 2},${cy} ${x + DIAMOND_SIZE},${cy + DIAMOND_SIZE}`
 }
 
@@ -354,6 +334,14 @@ function getRightDiamondPoints(bar: GanttBarModel): string {
 	return `${x - DIAMOND_SIZE * 2},${cy} ${x - DIAMOND_SIZE},${cy - DIAMOND_SIZE} ${x},${cy} ${x - DIAMOND_SIZE},${cy + DIAMOND_SIZE}`
 }
 
+function getParentDiamondFill(bar: GanttBarModel): string {
+	// Use a darker shade for contrast on the full-height bar
+	if (bar.meta?.color) {
+		return 'var(--white)'
+	}
+	return 'var(--white)'
+}
+
 function isPartialDate(bar: GanttBarModel) {
 	return bar.meta?.dateType === 'startOnly' || bar.meta?.dateType === 'endOnly'
 }
@@ -469,11 +457,6 @@ function startResize(bar: GanttBarModel, edge: 'start' | 'end', event: PointerEv
 	}
 }
 
-.gantt-indent-line {
-	pointer-events: none;
-	opacity: 0.5;
-}
-
 .gantt-collapse-toggle {
 	pointer-events: all;
 	cursor: pointer;