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/index.html

@@ -53,6 +53,7 @@
       <div class="side__nav">
         <button type="button" class="navrow" id="nav-scheduled" data-view="scheduled"><span class="navrow__icon"></span><span data-i18n>Scheduled</span></button>
         <button type="button" class="navrow" id="nav-files" data-view="files"><span class="navrow__icon"></span><span data-i18n>Files</span></button>
+        <button type="button" class="navrow" id="nav-archived" data-view="archived"><span class="navrow__icon"></span><span data-i18n>Archived</span></button>
       </div>
       <ul class="list" id="chat-list" aria-label="Chats" data-i18n-aria-label></ul>
       <div class="side__foot">
@@ -123,6 +124,15 @@
       <div class="page__body" id="scheduled-body"></div>
     </section>
 
+    <section class="page" id="page-archived" hidden aria-labelledby="archived-title">
+      <header class="head">
+        <h1 class="head__title" id="archived-title" data-i18n>Archived</h1>
+        <div class="head__place"></div>
+        <div class="head__tools"><button type="button" class="tool" id="archived-refresh" aria-label="Read again" title="Read again" data-i18n-aria-label data-i18n-title></button></div>
+      </header>
+      <div class="page__body" id="archived-body"></div>
+    </section>
+
     <section class="page settings" id="settings" hidden aria-labelledby="settings-title">
       <header class="head">
         <h1 class="head__title" id="settings-title" data-i18n>Settings</h1>