Add ability to select distance unit

lib/components/traction/traction_card.dart

@@ -1,5 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:mileograph_flutter/objects/objects.dart';
+import 'package:mileograph_flutter/services/distance_unit_service.dart';
+import 'package:provider/provider.dart';
 
 class TractionCard extends StatelessWidget {
   const TractionCard({
@@ -28,6 +30,7 @@ class TractionCard extends StatelessWidget {
     final domain = loco.domain ?? '';
     final hasMileageOrTrips = _hasMileageOrTrips(loco);
     final statusColors = _statusChipColors(context, status);
+    final distanceUnits = context.watch<DistanceUnitService>();
 
     return Card(
       child: Padding(
@@ -151,8 +154,11 @@ class TractionCard extends StatelessWidget {
               children: [
                 _statPill(
                   context,
-                  label: 'Miles',
-                  value: _formatNumber(loco.mileage),
+                  label: 'Distance',
+                  value: distanceUnits.format(
+                    loco.mileage ?? 0,
+                    decimals: 1,
+                  ),
                 ),
                 _statPill(
                   context,
@@ -203,6 +209,7 @@ Future<void> showTractionDetails(
   LocoSummary loco,
 ) async {
   final hasMileageOrTrips = _hasMileageOrTrips(loco);
+  final distanceUnits = context.read<DistanceUnitService>();
   await showModalBottomSheet(
     context: context,
     isScrollControlled: true,
@@ -275,7 +282,10 @@ Future<void> showTractionDetails(
                       _detailRow(
                         context,
                         'Mileage',
-                        _formatNumber(loco.mileage ?? 0),
+                        distanceUnits.format(
+                          loco.mileage ?? 0,
+                          decimals: 1,
+                        ),
                       ),
                       _detailRow(
                         context,
@@ -368,8 +378,3 @@ bool _hasMileageOrTrips(LocoSummary loco) {
   final trips = loco.trips ?? loco.journeys ?? 0;
   return mileage > 0 || trips > 0;
 }
-
-String _formatNumber(double? value) {
-  if (value == null) return '0';
-  return value.toStringAsFixed(1);
-}