Fixed horizontal scroll

lib/widgets/tasq_adaptive_list.dart

@@ -230,7 +230,18 @@ class TasQAdaptiveList<T> extends StatelessWidget {
       onRowTap: onRowTap,
     );
 
-    final contentWidth = constraints.maxWidth * 0.8;
+    // Use progressively smaller fractions of the viewport on larger screens
+    // so that content doesn't stretch too widely, but also consume as much
+    // width as possible when the display is more modest.
+    double contentFactor;
+    if (constraints.maxWidth < 1200) {
+      contentFactor = 0.95; // not-so-wide monitors
+    } else if (constraints.maxWidth < 1800) {
+      contentFactor = 0.85; // wide monitors
+    } else {
+      contentFactor = 0.75; // ultra-wide monitors
+    }
+    final contentWidth = constraints.maxWidth * contentFactor;
     final tableWidth = math.max(
       contentWidth,
       (columns.length + (rowActions == null ? 0 : 1)) * 140.0,
@@ -240,7 +251,15 @@ class TasQAdaptiveList<T> extends StatelessWidget {
       math.max(1, items.length),
     );
 
-    final tableWidget = SingleChildScrollView(
+    // wrap horizontal scroll with a visible scrollbar on desktop. the
+    // ScrollController is shared so the scrollbar has something to observe.
+    final horizontalController = ScrollController();
+    final tableWidget = Scrollbar(
+      controller: horizontalController,
+      thumbVisibility: true,
+      trackVisibility: true,
+      child: SingleChildScrollView(
+        controller: horizontalController,
         scrollDirection: Axis.horizontal,
         child: SizedBox(
           width: tableWidth,
@@ -261,6 +280,7 @@ class TasQAdaptiveList<T> extends StatelessWidget {
             source: dataSource,
           ),
         ),
+      ),
     );
 
     final summarySection = summaryDashboard == null
@@ -277,6 +297,7 @@ class TasQAdaptiveList<T> extends StatelessWidget {
       primary: true,
       child: Center(
         child: SizedBox(
+          key: const Key('adaptive_list_content'),
           width: contentWidth,
           child: Column(
             mainAxisSize: MainAxisSize.min,