fix(gantt): render done tasks with strikethrough and reduced opacity

The gantt chart rebuild lost the visual distinction for completed tasks.
Restore strikethrough on task labels and add reduced opacity on bars
for done tasks.

Regression introduced in the gantt chart rebuild in 5fc255cb3.

Resolves #2211

frontend/src/components/gantt/GanttRowBars.vue

@@ -24,6 +24,7 @@
 				:height="32"
 				:rx="4"
 				:fill="getBarFill(bar)"
+				:opacity="bar.meta?.isDone ? 0.5 : 1"
 				:stroke="getBarStroke(bar)"
 				:stroke-width="getBarStrokeWidth(bar)"
 				:stroke-dasharray="!bar.meta?.hasActualDates ? '5,5' : 'none'"
@@ -88,6 +89,7 @@
 				:y="24"
 				class="gantt-bar-text"
 				:fill="getBarTextColor(bar)"
+				:text-decoration="bar.meta?.isDone ? 'line-through' : 'none'"
 				:clip-path="`url(#clip-${bar.id})`"
 				aria-hidden="true"
 			>