fix: set PBS status to offline when connection fails (addresses #326)

When both GetVersion and GetDatastores fail for PBS, properly set the
Status field to 'offline' and ConnectionHealth to 'error'. This prevents
the red dot from appearing when the instance state is undefined.

internal/monitoring/monitor.go

@@ -1516,6 +1516,8 @@ func (m *Monitor) pollPBSInstance(ctx context.Context, instanceName string, clie
 				Msg("PBS connected (version unavailable but datastores accessible)")
 		} else {
 			// Both failed - PBS is offline
+			pbsInst.Status = "offline"
+			pbsInst.ConnectionHealth = "error"
 			monErr := errors.WrapConnectionError("get_pbs_version", instanceName, versionErr)
 			log.Error().Err(monErr).Str("instance", instanceName).Msg("Failed to connect to PBS")
 			m.state.SetConnectionHealth("pbs-"+instanceName, false)