feat: add PDF reports, timezone management, GPS QR codes, and fix GPS tracking gaps

Issue #1: QR button on GPS Devices tab for re-enrollment
Issue #2: App-wide timezone setting with TimezoneContext, useFormattedDate hook,
  and admin timezone selector. All date displays now respect the configured timezone.
Issue #3: PDF export for Accountability Roster using @react-pdf/renderer with
  professional styling matching VIPSchedulePDF. Added Signal send button.
Issue #4: Fixed GPS "teleporting" gaps - syncPositions now fetches position history
  per device instead of only latest position. Changed cron to every 30s, added
  unique constraint on deviceId+timestamp for deduplication, lowered min interval to 10s.

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

backend/src/gps/gps.service.ts

@@ -256,6 +256,44 @@ Note: GPS tracking is only active during shift hours (${settings.shiftStartHour}
     };
   }
 
+  /**
+   * Get QR code info for an already-enrolled device
+   */
+  async getDeviceQrInfo(driverId: string): Promise<{
+    driverName: string;
+    deviceIdentifier: string;
+    serverUrl: string;
+    qrCodeUrl: string;
+    updateIntervalSeconds: number;
+  }> {
+    const device = await this.prisma.gpsDevice.findUnique({
+      where: { driverId },
+      include: { driver: { select: { id: true, name: true } } },
+    });
+
+    if (!device) {
+      throw new NotFoundException('Driver is not enrolled for GPS tracking');
+    }
+
+    const settings = await this.getSettings();
+    const serverUrl = this.traccarClient.getDeviceServerUrl();
+
+    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', device.deviceIdentifier);
+    qrUrl.searchParams.set('interval', String(settings.updateIntervalSeconds));
+
+    return {
+      driverName: device.driver.name,
+      deviceIdentifier: device.deviceIdentifier,
+      serverUrl,
+      qrCodeUrl: qrUrl.toString(),
+      updateIntervalSeconds: settings.updateIntervalSeconds,
+    };
+  }
+
   /**
    * Unenroll a driver from GPS tracking
    */
@@ -562,7 +600,7 @@ Note: GPS tracking is only active during shift hours (${settings.shiftStartHour}
    * Sync positions from Traccar to our database (for history/stats)
    * Called periodically via cron job
    */
-  @Cron(CronExpression.EVERY_MINUTE)
+  @Cron(CronExpression.EVERY_30_SECONDS)
   async syncPositions(): Promise<void> {
     const devices = await this.prisma.gpsDevice.findMany({
       where: {
@@ -572,36 +610,51 @@ Note: GPS tracking is only active during shift hours (${settings.shiftStartHour}
 
     if (devices.length === 0) return;
 
-    try {
-      const positions = await this.traccarClient.getAllPositions();
+    const now = new Date();
 
-      for (const device of devices) {
-        const position = positions.find((p) => p.deviceId === device.traccarDeviceId);
-        if (!position) continue;
+    for (const device of devices) {
+      try {
+        // Calculate "since" from device's last active time with 5s overlap buffer
+        // Falls back to 2 minutes ago if no lastActive
+        const since = device.lastActive
+          ? new Date(device.lastActive.getTime() - 5000)
+          : new Date(now.getTime() - 120000);
 
-        // Update last active timestamp
+        const positions = await this.traccarClient.getPositionHistory(
+          device.traccarDeviceId,
+          since,
+          now,
+        );
+
+        if (positions.length === 0) continue;
+
+        // Batch insert with skipDuplicates (unique constraint on deviceId+timestamp)
+        await this.prisma.gpsLocationHistory.createMany({
+          data: positions.map((p) => ({
+            deviceId: device.id,
+            latitude: p.latitude,
+            longitude: p.longitude,
+            altitude: p.altitude || null,
+            speed: this.traccarClient.knotsToMph(p.speed || 0),
+            course: p.course || null,
+            accuracy: p.accuracy || null,
+            battery: p.attributes?.batteryLevel || null,
+            timestamp: new Date(p.deviceTime),
+          })),
+          skipDuplicates: true,
+        });
+
+        // Update lastActive to the latest position timestamp
+        const latestPosition = positions.reduce((latest, p) =>
+          new Date(p.deviceTime) > new Date(latest.deviceTime) ? p : latest
+        );
         await this.prisma.gpsDevice.update({
           where: { id: device.id },
-          data: { lastActive: new Date(position.deviceTime) },
-        });
-
-        // Store in history
-        await this.prisma.gpsLocationHistory.create({
-          data: {
-            deviceId: device.id,
-            latitude: position.latitude,
-            longitude: position.longitude,
-            altitude: position.altitude || null,
-            speed: this.traccarClient.knotsToMph(position.speed || 0),
-            course: position.course || null,
-            accuracy: position.accuracy || null,
-            battery: position.attributes?.batteryLevel || null,
-            timestamp: new Date(position.deviceTime),
-          },
+          data: { lastActive: new Date(latestPosition.deviceTime) },
         });
+      } catch (error) {
+        this.logger.error(`Failed to sync positions for device ${device.traccarDeviceId}: ${error}`);
       }
-    } catch (error) {
-      this.logger.error(`Failed to sync positions: ${error}`);
     }
   }