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.

.helloagents/CHANGELOG.md

@@ -4,3 +4,4 @@
 
 - 2026-03-25：初始化 `.helloagents/` 知识库骨架与首批模块文档，不代表源码功能变更。
 - 2026-03-25：新增 GHCR Docker 发布 workflow，并将 `docker-compose.yml` 的三个业务镜像切换到 `ghcr.io/micah123321/*`。
+- 2026-03-25：`/workspace` 默认布局改为“左侧 Workbench + 中央视终端 + 右侧状态监控”，并在状态监控中新增开机累计上下行流量展示。