fix: correct mock generator guest ID format to match alert system (addresses #441)

Mock VMs and containers were using 'node:qemu/vmid' format but the alert
system expects 'instance-node-vmid' format. This caused custom thresholds
to be ignored for mock guests.

internal/mock/generator.go

@@ -456,7 +456,7 @@ func generateVM(nodeName string, vmid int, config MockConfig) models.VM {
 		NetworkIn:  generateRealisticIO("network-in"),
 		NetworkOut: generateRealisticIO("network-out"),
 		Uptime:     uptime,
-		ID:         fmt.Sprintf("%s:qemu/%d", nodeName, vmid),
+		ID:         fmt.Sprintf("mock-%s-%d", nodeName, vmid),
 		Tags:       generateTags(),
 	}
 }
@@ -528,7 +528,7 @@ func generateContainer(nodeName string, vmid int, config MockConfig) models.Cont
 		NetworkIn:  generateRealisticIO("network-in-ct"),
 		NetworkOut: generateRealisticIO("network-out-ct"),
 		Uptime:     uptime,
-		ID:         fmt.Sprintf("%s:lxc/%d", nodeName, vmid),
+		ID:         fmt.Sprintf("mock-%s-%d", nodeName, vmid),
 		Tags:       generateTags(),
 	}
 }