Add ability to select distance unit

lib/components/pages/settings.dart

@@ -5,6 +5,7 @@ import 'package:go_router/go_router.dart';
 import 'package:http/http.dart' as http;
 import 'package:mileograph_flutter/services/authservice.dart';
 import 'package:mileograph_flutter/services/api_service.dart';
+import 'package:mileograph_flutter/services/distance_unit_service.dart';
 import 'package:mileograph_flutter/services/endpoint_service.dart';
 import 'package:mileograph_flutter/services/data_service.dart';
 import 'package:provider/provider.dart';
@@ -175,10 +176,11 @@ class _SettingsPageState extends State<SettingsPage> {
   @override
   Widget build(BuildContext context) {
     final endpointService = context.watch<EndpointService>();
+    final distanceUnitService = context.watch<DistanceUnitService>();
     final loggedIn = context.select<AuthService, bool>(
       (auth) => auth.isLoggedIn,
     );
-    if (!endpointService.isLoaded) {
+    if (!endpointService.isLoaded || !distanceUnitService.isLoaded) {
       return const Scaffold(
         body: Center(child: CircularProgressIndicator()),
       );
@@ -204,6 +206,34 @@ class _SettingsPageState extends State<SettingsPage> {
         child: Column(
           crossAxisAlignment: CrossAxisAlignment.start,
           children: [
+            Text(
+              'Distance units',
+              style: Theme.of(context).textTheme.titleMedium?.copyWith(
+                    fontWeight: FontWeight.w700,
+                  ),
+            ),
+            const SizedBox(height: 8),
+            Text(
+              'Choose how distances are displayed across the app.',
+              style: Theme.of(context).textTheme.bodySmall,
+            ),
+            const SizedBox(height: 12),
+            SegmentedButton<DistanceUnit>(
+              segments: DistanceUnit.values
+                  .map(
+                    (unit) => ButtonSegment<DistanceUnit>(
+                      value: unit,
+                      label: Text(unit.label),
+                    ),
+                  )
+                  .toList(),
+              selected: {distanceUnitService.unit},
+              onSelectionChanged: (selection) {
+                final next = selection.first;
+                distanceUnitService.setUnit(next);
+              },
+            ),
+            const SizedBox(height: 24),
             Text(
               'API endpoint',
               style: Theme.of(context).textTheme.titleMedium?.copyWith(