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/DriverChatModal.tsx

@@ -1,6 +1,7 @@
 import { useState, useEffect, useRef } from 'react';
 import { X, Send, Loader2 } from 'lucide-react';
 import { useDriverMessages, useSendMessage, useMarkMessagesAsRead } from '../hooks/useSignalMessages';
+import { useFormattedDate } from '@/hooks/useFormattedDate';
 
 interface Driver {
   id: string;
@@ -18,6 +19,7 @@ export function DriverChatModal({ driver, isOpen, onClose }: DriverChatModalProp
   const [message, setMessage] = useState('');
   const messagesEndRef = useRef<HTMLDivElement>(null);
   const inputRef = useRef<HTMLTextAreaElement>(null);
+  const { formatDateTime } = useFormattedDate();
 
   const { data: messages, isLoading } = useDriverMessages(driver?.id || null, isOpen);
   const sendMessage = useSendMessage();
@@ -66,22 +68,6 @@ export function DriverChatModal({ driver, isOpen, onClose }: DriverChatModalProp
     }
   };
 
-  const formatTime = (timestamp: string) => {
-    const date = new Date(timestamp);
-    const now = new Date();
-    const isToday = date.toDateString() === now.toDateString();
-
-    if (isToday) {
-      return date.toLocaleTimeString('en-US', { hour: 'numeric', minute: '2-digit' });
-    }
-    return date.toLocaleDateString('en-US', {
-      month: 'short',
-      day: 'numeric',
-      hour: 'numeric',
-      minute: '2-digit'
-    });
-  };
-
   return (
     <div className="fixed inset-0 z-50 flex items-center justify-center bg-black/50">
       <div
@@ -126,7 +112,7 @@ export function DriverChatModal({ driver, isOpen, onClose }: DriverChatModalProp
                     <p className={`text-[10px] mt-1 ${
                       msg.direction === 'OUTBOUND' ? 'text-primary-foreground/70' : 'text-muted-foreground/70'
                     }`}>
-                      {formatTime(msg.timestamp)}
+                      {formatDateTime(msg.timestamp)}
                     </p>
                   </div>
                 </div>