fix: 도넛 차트 maxVolume 복원 (최대값 유지, Volume 카드는 실시간)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/src/main/java/com/example/medilightv2android/ui/views/monitoring/PiezoMonitoringView.kt

@@ -768,7 +768,7 @@ fun PiezoMonitoringView(appState: AppState) {
                     BladdyRiveView(urgency = urgency, size = if (isCompact) 80.dp else 110.dp)
                     Spacer(modifier = Modifier.height(4.dp))
                     Text(
-                        if (lastVolumeMl > 0) "${"%.0f".format(lastVolumeMl)} ml" else "${appState.estimatedVolume} ml",
+                        if (maxVolumeMl > 0) "${"%.0f".format(maxVolumeMl)} ml" else "${appState.estimatedVolume} ml",
                         fontSize = 18.sp,
                         fontWeight = FontWeight.Bold,
                         color = urgency.accentColor,