Jump to the middle; bold jump arrows; Chicago time; demo hours 6 AM-9 PM

- Jump sheet: Top / Middle / Bottom with the Card fields arrows; the Jump
  button uses the same bold arrows.
- Container timezone defaults to America/Chicago (TZ in Dockerfile/compose).
- Demo worker follows its own business hours (Demo.BusinessHours, default
  06:00-21:00 every day) with the midnight pitstop; the simulated cycle in
  the browser shows the real worker's next run.

USMT-Worker.ps1

@@ -364,8 +364,8 @@ function Get-NextRunTime {
     $cycleSeconds = if ($config.IsDemo) { $config.Demo.CycleSeconds } else { $config.Worker.CycleSeconds }
     $nextRun = $now.AddSeconds($cycleSeconds)
 
-    $bh = $config.Worker.BusinessHours
-    if ($config.IsDemo -or -not $bh.Enabled) { return $nextRun }
+    $bh = if ($config.IsDemo) { $config.Demo.BusinessHours } else { $config.Worker.BusinessHours }
+    if (-not $bh -or -not $bh.Enabled) { return $nextRun }
 
     $startTime = [timespan]::Parse($bh.Start)
     $endTime = [timespan]::Parse($bh.End)