feat: SG Filter on/off 토글 추가 (Settings 패널)

- PiezoEchoAnalyzer.useSgFilter: true/false로 SG 필터 on/off
- OFF 시 raw ADC 그대로 low-echo detection에 사용
- Settings 패널에 Switch 토글 추가 (기본 ON)

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

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

@@ -213,9 +213,10 @@ class PiezoEchoAnalyzer private constructor() {
 
     // ── Denoising Pipeline ──
 
-    /** SG 디노이징 (6ch 알고리즘: TVD 제거, SG만 사용) */
+    var useSgFilter: Boolean = true
+
     fun denoise(signal: DoubleArray): DoubleArray {
-        return sgSmooth(signal)
+        return if (useSgFilter) sgSmooth(signal) else signal.copyOf()
     }
 
     /** 1D Total Variation Denoising — Chambolle (2004) dual projected gradient */

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

@@ -681,6 +681,26 @@ fun PiezoMonitoringView(appState: AppState) {
 
                         HorizontalDivider()
 
+                        // SG Filter toggle
+                        var sgEnabled by remember { mutableStateOf(analyzer.useSgFilter) }
+                        Row(
+                            modifier = Modifier.fillMaxWidth(),
+                            verticalAlignment = Alignment.CenterVertically
+                        ) {
+                            Text("SG Filter", fontSize = 14.sp, fontWeight = FontWeight.SemiBold)
+                            Spacer(modifier = Modifier.weight(1f))
+                            Switch(
+                                checked = sgEnabled,
+                                onCheckedChange = {
+                                    sgEnabled = it
+                                    analyzer.useSgFilter = it
+                                },
+                                colors = SwitchDefaults.colors(checkedTrackColor = MlPrimary)
+                            )
+                        }
+
+                        HorizontalDivider()
+
                         Row {
                             Text("Max Volume", fontSize = 14.sp, fontWeight = FontWeight.SemiBold)
                             Spacer(modifier = Modifier.weight(1f))