Show a full-screen result after every door action.

A 900ms row flash and a small bottom toast were too easy to miss at a
loud, dark door: staff could not tell at a glance whether the person in
front of them was in or not. Every action now ends on a screen that is
entirely green (checked in), red (already in, not found, write failed)
or amber (payment due), with the name and the detail staff need to
relay -- the check-in time, who did it, or the amount to collect.

It never holds the queue. Tapping anywhere closes it, it closes itself
after four seconds (six for the red ones, which carry a time or an
amount to read out), and a thin bar counts that down so the screen
vanishing never surprises anyone. Undo and Close are also explicit
buttons for staff who want them.

The undo affordance survives the close: the bottom Undo toast now
appears *after* the screen, for whatever remains of the ten-second
window, rather than alongside it -- react-hot-toast renders above the
overlay and would have floated a second Undo over the first. A write
that fails while the green screen is still up turns it red in place;
one that fails after the toast is up dismisses that toast, so staff are
never offered to undo something that never happened.

The old scanner's safe-area-top, pb-safe and animate-in classes were
undefined in this Tailwind config and silently ignored; the new screen
uses env(safe-area-inset-*) and a real transition instead.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

frontend/src/app/admin/scanner/_components/SessionSheet.tsx

@@ -21,6 +21,8 @@ export interface SessionEntry {
   entry: 'scan' | 'search' | 'walkin';
   method: DoorPaymentMethod | null;
   amount: number;
+  /** Epoch ms the action was fired; the undo window is measured from here. */
+  startedAt: number;
   undone: boolean;
   failed: boolean;
 }