feat(web): show active sandbox details in Box status popover

Display sandbox count and a detailed list of active sessions including
session ID, image, backend, resources (CPU/memory), network mode, and
last used time. Fetched from GET /api/v1/box/sessions in parallel.
Includes i18n for all 8 supported languages.

web/src/app/infra/http/BackendClient.ts

@@ -36,6 +36,7 @@ import {
   RerankModel,
   ApiRespPluginSystemStatus,
   ApiRespBoxStatus,
+  BoxSessionInfo,
   ApiRespMCPServers,
   ApiRespMCPServer,
   MCPServer,
@@ -894,6 +895,10 @@ export class BackendClient extends BaseHttpClient {
     return this.get('/api/v1/box/status');
   }
 
+  public getBoxSessions(): Promise<BoxSessionInfo[]> {
+    return this.get('/api/v1/box/sessions');
+  }
+
   // ============ User API ============
   public checkIfInited(): Promise<{ initialized: boolean }> {
     return this.get('/api/v1/user/init');