Address PR review: truncate error response logs and close http client

- Gate full error response body logging behind kDebugMode; truncate to
  500 chars in release builds to avoid log noise and data exposure
- Add RoutingService.close() and call from NavigationState.dispose()

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/services/routing_service.dart

@@ -30,7 +30,9 @@ class RoutingService {
   final http.Client _client;
 
   RoutingService({http.Client? client}) : _client = client ?? http.Client();
-  
+
+  void close() => _client.close();
+
   // Calculate route between two points using alprwatch
   Future<RouteResult> calculateRoute({
     required LatLng start,
@@ -80,7 +82,16 @@ class RoutingService {
       ).timeout(kNavigationRoutingTimeout);
 
       if (response.statusCode != 200) {
-        debugPrint('[RoutingService] Error response body: ${response.body}');
+        if (kDebugMode) {
+          debugPrint('[RoutingService] Error response body: ${response.body}');
+        } else {
+          const maxLen = 500;
+          final body = response.body;
+          final truncated = body.length > maxLen
+              ? '${body.substring(0, maxLen)}… [truncated]'
+              : body;
+          debugPrint('[RoutingService] Error response body ($maxLen char max): $truncated');
+        }
         throw RoutingException('HTTP ${response.statusCode}: ${response.reasonPhrase}');
       }
       

lib/state/navigation_state.dart

@@ -376,4 +376,10 @@ class NavigationState extends ChangeNotifier {
       notifyListeners();
     }
   }
+
+  @override
+  void dispose() {
+    _routingService.close();
+    super.dispose();
+  }
 }