fix(archive): keep the Moved to Archive toast off the next events

Centred at the bottom for eight seconds, the Undo toast sat over the
events moving up into the gap an ignored or completed row left. It now
sits in the bottom-right corner, lasts four seconds, and has an OK that
closes it without undoing. On a phone there is no side to clear and the
bottom is where an event's page ends, so it goes to the top, over the
header.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/redesign-checklist.test.tsx

@@ -86,6 +86,7 @@ test("a completed event shines and greys while it holds, then fades; an ignored
 import {
   ARCHIVE_COLLAPSE_MS,
   ARCHIVE_HOLD_MS,
+  ARCHIVE_UNDO_MS,
 } from "../src/client/components/redesign/ChecklistEvent.tsx";
 test("a completed event holds under a second, long enough for its shine, then collapses", () => {
   expect(ARCHIVE_HOLD_MS).toBe(900);
@@ -94,3 +95,8 @@ test("a completed event holds under a second, long enough for its shine, then co
   // The collapse waits out the 250 ms max-height transition.
   expect(ARCHIVE_COLLAPSE_MS - ARCHIVE_HOLD_MS).toBe(250);
 });
+test("the Moved to Archive notice offers Undo for four seconds, outlasting the row's collapse", () => {
+  // Halved from eight on 2026-11-10: the notice sat over the next events.
+  expect(ARCHIVE_UNDO_MS).toBe(4000);
+  expect(ARCHIVE_UNDO_MS).toBeGreaterThan(ARCHIVE_COLLAPSE_MS);
+});