fix: show subtasks in saved filter views regardless of parent presence

Add isFilteredView parameter to shouldShowTaskInListView() that skips
the parent-hiding logic when viewing tasks through a saved filter.
This ensures all filter-matching tasks are shown.

Ref: #2494

frontend/src/composables/useTaskListFiltering.ts

@@ -6,14 +6,24 @@ import type {ITask} from '@/modelTypes/ITask'
  * Subtasks are hidden only when their parent task is also in the current view
  * (same project). Cross-project subtasks remain visible.
  *
+ * In filtered views (saved filters), all tasks are shown regardless of parent
+ * presence, since the user explicitly filtered for them.
+ *
  * @param task - The task to check
  * @param allTasksInView - All tasks currently visible in the view
+ * @param isFilteredView - Whether the current view is a saved/custom filter
  * @returns true if the task should be shown, false if it should be hidden
  */
 export function shouldShowTaskInListView(
 	task: ITask,
 	allTasksInView: ITask[],
+	isFilteredView: boolean = false,
 ): boolean {
+	// In filtered views (saved filters), show all tasks that matched the filter
+	if (isFilteredView) {
+		return true
+	}
+
 	// If task has no parent, always show it
 	const parentTasksCount = task.relatedTasks?.parenttask?.length ?? 0
 	if (parentTasksCount === 0) {