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.

docker-compose.yml

@@ -8,6 +8,6 @@ services:
     restart: unless-stopped
     environment:
       - USMT_MODE=Demo
-      - TZ=UTC   # set your timezone, e.g. America/New_York
+      - TZ=America/Chicago   # timezone for every time shown (any IANA name, e.g. America/New_York)
     ports:
       - "8080:8080"