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.

web/layout.css

@@ -567,7 +567,10 @@ a.nav-brand:focus-visible { outline: 2px solid #3498db; outline-offset: 3px; }
     font: inherit; font-weight: 700; font-size: 0.9em; cursor: pointer; box-shadow: 0 6px 18px rgba(0,0,0,0.35);
 }
 .jump-btn[hidden] { display: none; }
-.jump-btn svg { width: 18px; height: 18px; }
+.jump-btn svg { width: 26px; height: 18px; }
+.jump-ends { gap: 8px; }
+.jump-end { display: inline-flex; align-items: center; justify-content: center; gap: 6px; font-weight: 600; }
+.jump-end svg { width: 17px; height: 17px; flex: none; }
 .jump-sheet .jump-search { margin: 8px 12px; font-size: 16px; }
 .jump-results, .jump-sections { overflow-y: auto; padding: 0 8px; }
 .jump-results { max-height: 38vh; }