Demo: migrations follow the schedule, worked by a simulated team

Each device now migrates on the day of its date tag instead of on a
looping 24-hour clock: earlier days are finished, today's devices go
through backup and restore during working hours, later days haven't
started. The few that don't finish have a cause the dashboard shows
(broken client, broken WMI, low disk, a USMT error, unreachable PC).

A simulated team keeps two weeks of working days tagged. During working
hours it adds devices, reschedules or drops one, tags stuck PCs with
their problem, then fixes them and moves them to a new day; each morning
finished days are closed out and a new day is scheduled. Actions print
in the worker terminal as [Team] lines. Settings live in Demo.Team.

The visitor sandbox now keeps per-tag edits laid over the live roster,
so the team's changes keep showing around a visitor's own edits.

Overview calendar: today is a filled badge on the date number, so it no
longer looks like the selected day (outline plus tint).

web/overview.css

@@ -123,8 +123,10 @@ table.ov-heat td { padding: 0; text-align: center; border: 0; background: none;
 .ov-day-bar { height: 6px; margin-top: 3px; }
 .ov-has-day { cursor: pointer; background: var(--bg-card); border: 1px solid var(--border-color); }
 .ov-has-day:hover, .ov-has-day:focus-visible, .ov-day.ov-selected { border-color: #3498db; box-shadow: 0 0 0 1px #3498db; }
-.ov-today { box-shadow: inset 0 0 0 2px #3498db; }
-.ov-today .ov-day-num { color: #3498db; font-weight: 700; }
+/* Today: the date number in a filled badge (like a calendar app), so it can't be mistaken for
+   the selected day, which gets the outline and a tint */
+.ov-today .ov-day-num { align-self: flex-start; background: #3498db; color: #fff; font-weight: 700; border-radius: 999px; min-width: 1.6em; padding: 0 0.4em; box-sizing: border-box; text-align: center; line-height: 1.55; }
+.ov-day.ov-selected { background: rgba(52,152,219,0.16); }
 
 
 /* tooltip */