Close door-screen toasts on our own timer so they dismiss on touchscreens.

react-hot-toast pauses every countdown while the pointer is inside the
Toaster and schedules no dismissal for toasts created while paused. On a
touchscreen, tapping the Undo button synthesizes a mouseenter with no
mouseleave, so the "Undone" toast never went away. Every toast on the
door screen now uses duration: Infinity and is closed by dismissAfter.

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

frontend/src/app/admin/scanner/_lib/feedback.ts

@@ -1,3 +1,5 @@
+import toast from 'react-hot-toast';
+
 // Haptic + audio confirmation. At a loud, dark door the sound and the buzz are
 // what staff actually register — the green flash is confirmation for the person
 // standing in front of them.
@@ -39,3 +41,18 @@ export function vibrate(pattern: number | number[]) {
     if (navigator.vibrate) navigator.vibrate(pattern);
   } catch {}
 }
+
+/**
+ * Dismiss a toast after `ms` regardless of react-hot-toast's hover/touch pause.
+ *
+ * The <Toaster> pauses every countdown while the pointer is "inside" its
+ * container, and schedules no dismissal at all for toasts created while paused.
+ * On a touchscreen, tapping a toast button (the Undo toast) synthesizes a
+ * mouseenter with no mouseleave until the next tap somewhere else — so the
+ * "Undone" toast that follows would sit there indefinitely. Callers create the
+ * toast with `duration: Infinity` and let this timer close it.
+ */
+export function dismissAfter(id: string, ms: number): string {
+  window.setTimeout(() => toast.dismiss(id), ms);
+  return id;
+}