Library upload, new folder, rename and delete; a chat's tools and skills (/scope)

Files -> Server writes through /api/v2/files/{upload,mkdir,rename} and
DELETE /files (the trash); upload is a Rust command (library_upload) that
picks files in the system dialog and sends them multipart in the field
`files`. A chat's menu opens Tools and skills..., the web's chat-settings
switches over GET/POST /chats/{id}/scope and /allow/clear. A popover can
open at a context menu's point.

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

ui/index.html

@@ -109,8 +109,11 @@
         <section class="files__pane" id="pane-server" hidden aria-label="Server" data-i18n-aria-label>
           <div class="files__head">
             <div class="files__where muted" id="server-where"></div>
+            <button type="button" class="tool" id="server-upload" aria-label="Upload" title="Upload" data-i18n-aria-label data-i18n-title></button>
+            <button type="button" class="tool" id="server-mkdir" aria-label="New folder" title="New folder" data-i18n-aria-label data-i18n-title></button>
             <button type="button" class="tool" id="server-refresh" aria-label="Read again" title="Read again" data-i18n-aria-label data-i18n-title></button>
           </div>
+          <p class="status" id="server-status" hidden></p>
           <div class="files__tree" id="server-tree"></div>
         </section>
       </div>