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/backend/src/services/status-monitor.service.ts

@@ -18,6 +18,8 @@ interface ServerStatus {
     cpuModel?: string;
     netRxRate?: number; // Bytes per second
     netTxRate?: number; // Bytes per second
+    netRxTotalBytes?: number; // Bytes since boot
+    netTxTotalBytes?: number; // Bytes since boot
     netInterface?: string;
     osName?: string;
     loadAvg?: number[]; // 系统平均负载 [1min, 5min, 15min]
@@ -318,6 +320,8 @@ export class StatusMonitorService {
                          status.netInterface = defaultInterface;
                          const currentRx = currentStats[defaultInterface].rx_bytes;
                          const currentTx = currentStats[defaultInterface].tx_bytes;
+                         status.netRxTotalBytes = currentRx;
+                         status.netTxTotalBytes = currentTx;
                          const prevStats = previousNetStats.get(sessionId);
 
                          if (prevStats && prevStats.timestamp < timestamp) {