feat(workspace): add workbench layout and traffic totals

Rework the default /workspace layout into a three-column view
with a left-side Workbench, centered terminal, and right-side
status monitor.

Add a new Workbench pane that groups file manager, command
history, and editor into tabs while preserving panel state.
Extend server status data to expose cumulative network upload
and download totals since boot, and show them in the monitor.

Include a lightweight migration for the old default layout and
update related locale strings, pane metadata, and knowledge
base records.

packages/frontend/src/components/LayoutConfigurator.vue

@@ -163,6 +163,7 @@ const paneLabels = computed(() => ({ // Assuming labels might depend on i18n
   commandBar: t('layout.pane.commandBar', '命令栏'),
   fileManager: t('layout.pane.fileManager', '文件管理器'),
   editor: t('layout.pane.editor', '编辑器'),
+  workbench: t('layout.pane.workbench', '工作台'),
   statusMonitor: t('layout.pane.statusMonitor', '状态监视器'),
   commandHistory: t('layout.pane.commandHistory', '命令历史'),
   quickCommands: t('layout.pane.quickCommands', '快捷指令'),