fix: prevent GPS map from resetting zoom/position on data refresh

The MapFitBounds component was calling fitBounds on every 30-second
location refresh, overriding the user's current view. Now only fits
bounds on the initial load so users can pan and zoom freely without
interruption.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/pages/GpsTracking.tsx

@@ -1,4 +1,4 @@
-import { useState, useEffect, useMemo } from 'react';
+import { useState, useEffect, useRef, useMemo } from 'react';
 import { MapContainer, TileLayer, Marker, Popup, useMap } from 'react-leaflet';
 import L from 'leaflet';
 import 'leaflet/dist/leaflet.css';
@@ -85,17 +85,21 @@ const createDriverIcon = (isActive: boolean) => {
   });
 };
 
-// Map auto-fit component
+// Map auto-fit component — only fits bounds on initial load, not on every refresh
 function MapFitBounds({ locations }: { locations: DriverLocation[] }) {
   const map = useMap();
+  const hasFitted = useRef(false);
 
   useEffect(() => {
+    if (hasFitted.current) return;
+
     const validLocations = locations.filter(d => d.location);
     if (validLocations.length > 0) {
       const bounds = L.latLngBounds(
         validLocations.map(loc => [loc.location!.latitude, loc.location!.longitude])
       );
       map.fitBounds(bounds, { padding: [50, 50], maxZoom: 14 });
+      hasFitted.current = true;
     }
   }, [locations, map]);