fix: keep the network chart tooltip inside the screen

The tooltip for edge bars rendered past the phone bounds. Clamp the
bubble with fitInsideHorizontally/Vertically and cap its width so it
always stays within the chart.

lib/features/settings/presentation/widgets/network_usage_chart.dart

@@ -247,6 +247,11 @@ class _NetworkUsageChartState extends State<NetworkUsageChart> {
                       vertical: AppSpacing.sm,
                     ),
                     tooltipMargin: AppSpacing.sm,
+                    // Edge bars sit under the screen edge — clamp the bubble
+                    // inside the chart so it never spills off the phone.
+                    maxContentWidth: 200,
+                    fitInsideHorizontally: true,
+                    fitInsideVertically: true,
                     getTooltipItem: (group, groupIndex, rod, rodIndex) {
                       final sample = samples[group.x];
                       final lines = StringBuffer(_taipeiLabel(sample.hour));

test/features/settings/presentation/widgets/network_usage_chart_test.dart

@@ -74,6 +74,12 @@ void main() {
     expect(find.text('1日8時'), findsOneWidget);
     // Labels are spaced out, not one per bar: 24 h at every 6 → 4 labels.
     expect(find.textContaining('日'), findsNWidgets(4));
+    // The tooltip clamps inside the chart so an edge bar never spills off the
+    // phone screen.
+    final tooltip = data.barTouchData.touchTooltipData;
+    expect(tooltip.fitInsideHorizontally, isTrue);
+    expect(tooltip.fitInsideVertically, isTrue);
+    expect(tooltip.maxContentWidth, 200);
   });
 
   testWidgets('switching to 7d shows 28 six-hour buckets', (tester) async {