Add settings page with synced appearance and password change

- Store app settings as one JSON document on the server, merged per key and
  pushed to other devices; cache locally to avoid a flash on load
- Settings page groups appearance, account, shortcuts, shares, API tokens and
  trash; full screen with a section list on phones
- Font size and content width settings
- Change the login password, signing out other sessions
- Settings writes and password changes only accept a login session

web/src/app/Sidebar.vue

@@ -44,7 +44,7 @@ function onRootDrop(e: DragEvent) {
     </div>
     <div class="rm-sidebar-foot">
       <button class="rm-foot-btn" title="命令面板（F1）" @click="ws.switcher = '>'"><Icon name="command" />命令</button>
-      <button class="rm-foot-btn" @click="ws.trashOpen = true"><Icon name="trash" />回收站</button>
+      <button class="rm-foot-btn" title="设置（Ctrl+,）" @click="ws.settings = 'index'"><Icon name="settings" />设置</button>
       <button class="rm-foot-btn" @click="emit('logout')"><Icon name="logout" />退出</button>
     </div>
   </div>