Improve desktop geolocation handling

src/uk_bus_stops/static/app.js

@@ -605,8 +605,17 @@ byId('locate-button').addEventListener('click', () => {
       const apiParams = new URLSearchParams({...coordinates, label: 'Your location'});
       loadUrl(`${API_URLS.stops}?${apiParams}`);
     },
-    () => { setLoading(false); showError('Location access was denied or unavailable.'); },
-    {enableHighAccuracy: true, timeout: 10000}
+    error => {
+      setLoading(false);
+      const messages = {
+        1: 'Location permission was denied. Check this site’s location permission in your browser.',
+        2: 'Your browser could not determine your location. Check that device or operating-system location services are enabled.',
+        3: 'Determining your location timed out. Try again, or enter latitude and longitude manually.',
+      };
+      showError(messages[error.code] || `Could not determine your location${error.message ? `: ${error.message}` : '.'}`);
+    },
+    // Desktop browsers usually rely on network location rather than GPS.
+    {enableHighAccuracy: false, timeout: 20000, maximumAge: 300000}
   );
 });