fix(dashboard): add aggregated resource usage stats to the dashboard

- Aggregate CPU, memory, and network stats across all running containers
- Extend ISystemStatus.docker with resource usage fields
- Fix getContainerStats Swarm service ID fallback
- Wire dashboard resource usage card to real backend data

ts_interfaces/data/system.ts

@@ -8,6 +8,11 @@ export interface ISystemStatus {
   docker: {
     running: boolean;
     version: unknown;
+    cpuUsage: number;
+    memoryUsage: number;
+    memoryTotal: number;
+    networkIn: number;
+    networkOut: number;
   };
   reverseProxy: {
     http: { running: boolean; port: number };