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>

docs/PRD.md

@@ -193,7 +193,8 @@ the cut are still counted in the header, still on the timeline, and one tap away
 **F3 — Mark completed.**
 Done writes durable progress and a metadata snapshot immediately. A confirmation remains for about
 0.9 seconds (1.5 until 2026-10-20, which read as unresponsive) before the row fades/collapses into
-Archive. Undo is available for eight seconds; Archive Restore remains available afterwards. A failed
+Archive. Undo is offered in a toast, out of the list's way, for four seconds (eight until 2026-11-10, when it sat
+over the next events), and its OK closes it sooner; Archive Restore remains available afterwards. A failed
 write is disclosed and never presented as saved. Reduced motion removes the fade.
 
 **F4 — Settings and visibility.**