fix: 도넛차트 캐릭터 옆 ml을 max volume으로 변경

lastVolumeMl (마지막 측정) → maxVolumeMl (최대 측정값)
세션 중 가장 높은 측정값을 표시

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

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

@@ -749,7 +749,7 @@ fun PiezoMonitoringView(appState: AppState) {
                     BladdyRiveView(urgency = urgency, size = if (isCompact) 70.dp else 100.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 = 16.sp,
                         fontWeight = FontWeight.Bold,
                         color = urgency.accentColor,