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>

frontend/src/components/DriverScheduleModal.tsx

@@ -3,6 +3,7 @@ import { api } from '@/lib/api';
 import { X, Calendar, Clock, MapPin, Car, User, ChevronLeft, ChevronRight } from 'lucide-react';
 import { Driver } from '@/types';
 import { useState } from 'react';
+import { useFormattedDate } from '@/hooks/useFormattedDate';
 
 interface ScheduleEvent {
   id: string;
@@ -36,6 +37,7 @@ interface DriverScheduleModalProps {
 
 export function DriverScheduleModal({ driver, isOpen, onClose }: DriverScheduleModalProps) {
   const [selectedDate, setSelectedDate] = useState(new Date());
+  const { formatDate, formatTime } = useFormattedDate();
 
   const dateString = selectedDate.toISOString().split('T')[0];
 
@@ -85,23 +87,6 @@ export function DriverScheduleModal({ driver, isOpen, onClose }: DriverScheduleM
 
   const isToday = selectedDate.toDateString() === new Date().toDateString();
 
-  const formatTime = (dateString: string) => {
-    return new Date(dateString).toLocaleTimeString('en-US', {
-      hour: 'numeric',
-      minute: '2-digit',
-      hour12: true,
-    });
-  };
-
-  const formatDate = (date: Date) => {
-    return date.toLocaleDateString('en-US', {
-      weekday: 'long',
-      month: 'long',
-      day: 'numeric',
-      year: 'numeric',
-    });
-  };
-
   const getStatusColor = (status: string) => {
     switch (status) {
       case 'COMPLETED':