feat: add QR code to enrollment screen for Traccar Client setup

Generate a QR code URL containing device ID, server URL, and update
interval that the Traccar Client app can scan to auto-configure.
The enrollment modal now shows the QR prominently with manual setup
collapsed as a fallback. Also pins Traccar to 6.11 and fixes Docker
health checks (IPv6/curl issues).

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

backend/src/gps/gps.service.ts

@@ -5,6 +5,7 @@ import {
   BadRequestException,
   OnModuleInit,
 } from '@nestjs/common';
+import { ConfigService } from '@nestjs/config';
 import { Cron, CronExpression } from '@nestjs/schedule';
 import { PrismaService } from '../prisma/prisma.service';
 import { SignalService } from '../signal/signal.service';
@@ -27,6 +28,7 @@ export class GpsService implements OnModuleInit {
     private prisma: PrismaService,
     private traccarClient: TraccarClientService,
     private signalService: SignalService,
+    private configService: ConfigService,
   ) {}
 
   async onModuleInit() {
@@ -141,6 +143,7 @@ export class GpsService implements OnModuleInit {
     success: boolean;
     deviceIdentifier: string;
     serverUrl: string;
+    qrCodeUrl: string;
     instructions: string;
     signalMessageSent?: boolean;
   }> {
@@ -192,6 +195,19 @@ export class GpsService implements OnModuleInit {
     const serverUrl = this.traccarClient.getDeviceServerUrl();
     const settings = await this.getSettings();
 
+    // Build QR code URL for Traccar Client app
+    // Format: https://server:5055?id=DEVICE_ID&interval=SECONDS
+    // The Traccar Client app parses this as: server URL (origin) + query params (id, interval, etc.)
+    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));
+    const qrCodeUrl = qrUrl.toString();
+
+    this.logger.log(`QR code URL for driver: ${qrCodeUrl}`);
+
     const instructions = `
 GPS Tracking Setup Instructions for ${driver.name}:
 
@@ -234,6 +250,7 @@ Note: GPS tracking is only active during shift hours (${settings.shiftStartHour}
       success: true,
       deviceIdentifier: actualDeviceId, // Return what Traccar actually stored
       serverUrl,
+      qrCodeUrl,
       instructions,
       signalMessageSent,
     };