Archived chats: a page to find them again, Restore chat, delete

Archive was one-way in the app. Archived (sidebar, under Files) reads
GET /api/v2/chats?archived=true, newest first and paged; a row opens the
chat, Restore chat PATCHes archived:false and reads the sidebar again, and
the row's menu deletes. An open archived chat says so in its header, with
Restore chat there and in its menu. The words are the web's own ("Archived",
"Restore chat"). Tests: D2 at 1280 and 390 px.

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

ui/js/dom.js

@@ -99,6 +99,7 @@ export const ICONS = {
   user: ["M8 2a3 3 0 110 6 3 3 0 010-6zm0 1.5a1.5 1.5 0 100 3 1.5 1.5 0 000-3z", "M2.5 14c0-2.9 2.4-4.75 5.5-4.75S13.5 11.1 13.5 14H12c0-2-1.65-3.25-4-3.25S4 12 4 14z"],
   check: "M6.5 10.4l6-6 1.06 1.06L6.5 12.53 2.94 8.97 4 7.9z",
   bell: ["M8 1.5a4.5 4.5 0 014.5 4.5v3l1.5 2.5H2L3.5 9V6A4.5 4.5 0 018 1.5zM8 3a3 3 0 00-3 3v3.42l-.35.58h6.7L11 9.42V6a3 3 0 00-3-3z", "M6.25 12.5h3.5a1.75 1.75 0 01-3.5 0z"],
+  archive: ["M1.5 2.5h13v3.5h-13zM3 4v.5h10V4z", "M2.5 6.5H4V12h8V6.5h1.5v7h-11z", "M6 7.5h4V9H6z"],
   info: ["M8 1.5a6.5 6.5 0 110 13 6.5 6.5 0 010-13zM8 3a5 5 0 100 10A5 5 0 008 3z", "M7.25 7h1.5v4.5h-1.5zM7.25 4.5h1.5V6h-1.5z"],
 }