feat: Settings에 Low Echo Threshold + Distance/Sample 슬라이더 추가

1. Low Echo Threshold: 800~2000 슬라이더 (기본 1150, 주황색)
   → GreenZoneConstants.lowEchoAmp 런타임 변경
   → CH4/CH5 threshold 조절로 lateral 감지 개선

2. Distance/Sample: 1.5~2.5mm 슬라이더 (기본 1.771, 초록색)
   → PiezoHW.distancePerSample 런타임 변경
   → 기기별 캘리브레이션 가능

3. 도넛차트 ml 실시간 표시: estimatedVolume → lastVolumeMl 직접 표시
   → 측정 즉시 정확한 ml 반영 (기존: 레벨 변환 후 재계산으로 지연)

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

app/src/main/java/com/example/medilightv2android/managers/GreenZoneConstants.kt

@@ -38,7 +38,7 @@ object GreenZoneConstants {
      *  UrinAI의 liquidThrLoose(raw 기준)와 다름 — 여기는 TVD+SG 적용 후 신호 기준.
      *  Python 원본: 1150 (low_echo_detection_method_b.py LOW_ECHO_AMP, 6ch 버전)
      *  영향: PiezoEchoAnalyzer → low-echo span 탐지, 벽 찾기의 기반 */
-    const val lowEchoAmp: Float = 1150f
+    var lowEchoAmp: Float = 1150f
 
     /** 구조 이진화 임계값: raw < 이 값 → 액체(liquid), ≥ → 조직(tissue).
      *  낮출수록 엄격 (더 확실한 액체만 인정), 높일수록 관대.

app/src/main/java/com/example/medilightv2android/managers/PiezoBVEstimator.kt

@@ -90,8 +90,8 @@ object PiezoHW {
     val degree: DoubleArray get() = centerCh.map { degreeAll[it] }.toDoubleArray()
     val degreeLR: DoubleArray get() = centerCh.map { degreeLRAll[it] }.toDoubleArray()
 
-    /** Acoustic calibration */
+    /** Acoustic calibration (런타임 조절 가능) */
-    const val distancePerSample: Double = 1.771   // mm/sample
+    var distancePerSample: Double = 1.771   // mm/sample
     const val delayOffsetMm: Double = 6.85
 
     /** Volume model */

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

@@ -42,6 +42,8 @@ import com.example.medilightv2android.ble.BleManager
 import com.example.medilightv2android.ble.PiezoChannelData
 import com.example.medilightv2android.managers.PiezoEchoAnalyzer
 import com.example.medilightv2android.managers.PiezoConstants
+import com.example.medilightv2android.managers.GreenZoneConstants
+import com.example.medilightv2android.managers.PiezoHW
 import com.example.medilightv2android.managers.estimateBladderVolume6ch
 import com.example.medilightv2android.models.BladderLevel
 import com.example.medilightv2android.models.UrgencyLevel
@@ -624,7 +626,8 @@ fun PiezoMonitoringView(appState: AppState) {
                     colors = CardDefaults.cardColors(containerColor = MlCardBackground),
                     modifier = Modifier.shadow(8.dp, RoundedCornerShape(16.dp), spotColor = Color.Black.copy(alpha = 0.06f))
                 ) {
-                    Column(modifier = Modifier.padding(20.dp)) {
+                    Column(modifier = Modifier.padding(20.dp), verticalArrangement = Arrangement.spacedBy(8.dp)) {
+                        // Catheterization Threshold
                         Row(verticalAlignment = Alignment.CenterVertically) {
                             Text("Catheterization Threshold", fontSize = 14.sp, fontWeight = FontWeight.SemiBold)
                             Spacer(modifier = Modifier.weight(1f))
@@ -637,8 +640,47 @@ fun PiezoMonitoringView(appState: AppState) {
                             steps = 8,
                             colors = SliderDefaults.colors(thumbColor = MlPrimary, activeTrackColor = MlPrimary)
                         )
+
                         HorizontalDivider()
-                        Spacer(modifier = Modifier.height(8.dp))
+
+                        // Low Echo Threshold
+                        var currentThreshold by remember { mutableStateOf(GreenZoneConstants.lowEchoAmp) }
+                        Row(verticalAlignment = Alignment.CenterVertically) {
+                            Text("Low Echo Threshold", fontSize = 14.sp, fontWeight = FontWeight.SemiBold)
+                            Spacer(modifier = Modifier.weight(1f))
+                            Text("${"%.0f".format(currentThreshold)}", fontSize = 14.sp, fontWeight = FontWeight.Bold, color = Color(0xFFFF9500))
+                        }
+                        Slider(
+                            value = currentThreshold,
+                            onValueChange = {
+                                currentThreshold = it
+                                GreenZoneConstants.lowEchoAmp = it
+                            },
+                            valueRange = 800f..2000f,
+                            colors = SliderDefaults.colors(thumbColor = Color(0xFFFF9500), activeTrackColor = Color(0xFFFF9500))
+                        )
+
+                        HorizontalDivider()
+
+                        // Distance Per Sample
+                        var currentDps by remember { mutableStateOf(PiezoHW.distancePerSample.toFloat()) }
+                        Row(verticalAlignment = Alignment.CenterVertically) {
+                            Text("Distance/Sample", fontSize = 14.sp, fontWeight = FontWeight.SemiBold)
+                            Spacer(modifier = Modifier.weight(1f))
+                            Text("${"%.3f".format(currentDps)} mm", fontSize = 14.sp, fontWeight = FontWeight.Bold, color = Color(0xFF4CAF50))
+                        }
+                        Slider(
+                            value = currentDps,
+                            onValueChange = {
+                                currentDps = it
+                                PiezoHW.distancePerSample = it.toDouble()
+                            },
+                            valueRange = 1.5f..2.5f,
+                            colors = SliderDefaults.colors(thumbColor = Color(0xFF4CAF50), activeTrackColor = Color(0xFF4CAF50))
+                        )
+
+                        HorizontalDivider()
+
                         Row {
                             Text("Max Volume", fontSize = 14.sp, fontWeight = FontWeight.SemiBold)
                             Spacer(modifier = Modifier.weight(1f))
@@ -673,7 +715,7 @@ fun PiezoMonitoringView(appState: AppState) {
                     BladdyRiveView(urgency = urgency, size = if (isCompact) 70.dp else 100.dp)
                     Spacer(modifier = Modifier.height(4.dp))
                     Text(
-                        "${appState.estimatedVolume} ml",
+                        if (lastVolumeMl > 0) "${"%.0f".format(lastVolumeMl)} ml" else "${appState.estimatedVolume} ml",
                         fontSize = 16.sp,
                         fontWeight = FontWeight.Bold,
                         color = urgency.accentColor,