fix: optimize Traccar Client QR code with iOS background GPS settings

QR enrollment was only setting id and interval, causing iOS to default
to medium accuracy with stop_detection enabled — which pauses GPS
updates when the phone appears stationary, causing 5-30 min gaps.

Now sets accuracy=highest, stop_detection=false, distance=0, angle=30,
heartbeat=300, buffer=true. Also updates driver instructions with
required iPhone settings (Always location, Background App Refresh).

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

backend/src/gps/gps.service.ts

@@ -198,14 +198,20 @@ export class GpsService implements OnModuleInit {
     const settings = await this.getSettings();
 
     // Build QR code URL for Traccar Client app
-    // Format: https://server:5055?id=DEVICE_ID&interval=SECONDS
+    // All supported params: id, interval, accuracy, distance, angle, heartbeat, buffer, stop_detection, wakelock
-    // The Traccar Client app parses this as: server URL (origin) + query params (id, interval, etc.)
+    // Key iOS settings: accuracy=highest + stop_detection=false prevents iOS from pausing GPS updates
     const devicePort = this.configService.get<number>('TRACCAR_DEVICE_PORT') || 5055;
     const traccarPublicUrl = this.traccarClient.getTraccarUrl();
     const qrUrl = new URL(traccarPublicUrl);
     qrUrl.port = String(devicePort);
     qrUrl.searchParams.set('id', actualDeviceId);
     qrUrl.searchParams.set('interval', String(settings.updateIntervalSeconds));
+    qrUrl.searchParams.set('accuracy', 'highest');       // iOS: kCLDesiredAccuracyBestForNavigation
+    qrUrl.searchParams.set('distance', '0');              // Disable distance filter — rely on interval
+    qrUrl.searchParams.set('angle', '30');                // Send update on 30° heading change (turns)
+    qrUrl.searchParams.set('heartbeat', '300');           // 5 min heartbeat when stationary
+    qrUrl.searchParams.set('stop_detection', 'false');    // CRITICAL: prevent iOS from pausing GPS
+    qrUrl.searchParams.set('buffer', 'true');             // Buffer points when offline
     const qrCodeUrl = qrUrl.toString();
 
     this.logger.log(`QR code URL for driver: ${qrCodeUrl}`);
@@ -217,15 +223,21 @@ GPS Tracking Setup Instructions for ${driver.name}:
    - iOS: https://apps.apple.com/app/traccar-client/id843156974
    - Android: https://play.google.com/store/apps/details?id=org.traccar.client
 
-2. Open the app and configure:
+2. Open the app and scan the QR code (or configure manually):
    - Device identifier: ${actualDeviceId}
    - Server URL: ${serverUrl}
+   - Location accuracy: Highest
    - Frequency: ${settings.updateIntervalSeconds} seconds
-   - Location accuracy: High
+   - Distance: 0
+   - Angle: 30
 
-3. Tap "Service Status" to start tracking.
+3. IMPORTANT iPhone Settings:
+   - Settings > Privacy > Location Services > Traccar Client > "Always"
+   - Settings > General > Background App Refresh > ON for Traccar Client
+   - Do NOT swipe the app away from the app switcher
+   - Low Power Mode should be OFF while driving
 
-Note: GPS tracking is only active during shift hours (${settings.shiftStartHour}:00 - ${settings.shiftEndHour}:00).
+4. Tap "Service Status" to start tracking.
     `.trim();
 
     let signalMessageSent = false;
@@ -286,6 +298,12 @@ Note: GPS tracking is only active during shift hours (${settings.shiftStartHour}
     qrUrl.port = String(devicePort);
     qrUrl.searchParams.set('id', device.deviceIdentifier);
     qrUrl.searchParams.set('interval', String(settings.updateIntervalSeconds));
+    qrUrl.searchParams.set('accuracy', 'highest');
+    qrUrl.searchParams.set('distance', '0');
+    qrUrl.searchParams.set('angle', '30');
+    qrUrl.searchParams.set('heartbeat', '300');
+    qrUrl.searchParams.set('stop_detection', 'false');
+    qrUrl.searchParams.set('buffer', 'true');
 
     return {
       driverName: device.driver.name,