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>
