refactor: rename deviceInfo lastUpdated to lastSynced, add firstDiscovered

Aligns DeviceInfo model with console discovery-timestamp changes. Type-only field; not rendered, so no runtime dependency on the API change.

Related to device-management-toolkit/rpc-go#1394

Author: sinchubhat

src/models/models.ts

@@ -31,7 +31,8 @@ export interface DeviceInfo {
   currentMode: string
   features: string
   ipAddress: string
-  lastUpdated?: Date
+  firstDiscovered?: Date
+  lastSynced?: Date
 }
 export interface DeviceStats {
   totalCount: number