Fix Google Maps async loading parameter

Add loading=async query parameter to Google Maps API URL to prevent
synchronous DOM manipulation. This fixes the warning:
'Google Maps JavaScript API has been loaded directly without loading=async'

The loading=async parameter tells Google Maps to defer API initialization
until the script is fully loaded, preventing race conditions with React's
DOM management.

🤖 Generated with Claude Code

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

frontend/src/features/stations/utils/maps-loader.ts

@@ -37,7 +37,7 @@ export function loadGoogleMaps(): Promise<void> {
 
     // Create script tag
     const script = document.createElement('script');
-    script.src = `https://maps.googleapis.com/maps/api/js?key=${apiKey}&libraries=places`;
+    script.src = `https://maps.googleapis.com/maps/api/js?key=${apiKey}&loading=async&libraries=places`;
     script.async = true;
     script.defer = true;