UX: Placement 자동스캔 + Stop/Resume 삭제 + Placement Complete

Placement:
- 화면 진입 시 자동 스캔 시작 (isContinuousMode=true)
- 초기 힌트: "센서를 부착해주세요"
- Stop/Resume Scanning 버튼 삭제
- Start Measurement → "Placement Complete" (Green 또는 4+ch 감지 시 활성화)
- Skip 버튼 TextButton으로 유지

Algorithm:
- LATERAL 조건: (ch4&&ch5) OR 제거 → lrSymmetry >= 0.7 필수

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

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

@@ -59,10 +59,10 @@ fun PlacementGuideView(appState: AppState) {
     val analyzer = remember { PiezoEchoAnalyzer.shared }
 
     var isScanning by remember { mutableStateOf(false) }
-    var isContinuousMode by remember { mutableStateOf(false) }
+    var isContinuousMode by remember { mutableStateOf(true) }
     val channelDetected = remember { mutableStateListOf(false, false, false, false, false, false) }
     val channelUrineLen = remember { mutableStateListOf(0, 0, 0, 0, 0, 0) }
-    var directionHint by remember { mutableStateOf("치골 위에 센서를 올려놓으세요") }
+    var directionHint by remember { mutableStateOf("센서를 부착해주세요") }
     var directionIcon by remember { mutableStateOf("") }
     var placementScore by remember { mutableIntStateOf(0) }
     var scanCount by remember { mutableIntStateOf(0) }
@@ -82,7 +82,7 @@ fun PlacementGuideView(appState: AppState) {
         isLocked = false
         scanCount = 0
         placementScore = 0
-        directionHint = "치골 위에 센서를 올려놓으세요"
+        directionHint = "센서를 부착해주세요"
         directionIcon = ""
         for (i in 0 until 6) { channelDetected[i] = false; channelUrineLen[i] = 0 }
     }
@@ -573,75 +573,30 @@ fun PlacementGuideView(appState: AppState) {
                 }
             }
 
-            // Start/Stop button
+            // Placement Complete button
             Button(
                 onClick = {
-                    if (isContinuousMode) {
                     isContinuousMode = false
-                    } else {
-                        isContinuousMode = true
-                    }
+                    appState.placementComplete()
                 },
+                enabled = isLocked || detectedCount >= 4,
                 modifier = Modifier
                     .fillMaxWidth()
                     .height(52.dp),
                 shape = RoundedCornerShape(14.dp),
                 colors = ButtonDefaults.buttonColors(
-                    containerColor = if (isContinuousMode) Color.Red else MlPrimary
+                    containerColor = if (isLocked) Color(0xFF4CAF50) else MlPrimary,
+                    disabledContainerColor = Color.Gray.copy(alpha = 0.3f)
                 )
             ) {
-                Text(
-                    text = when {
-                        isContinuousMode -> "Stop Scanning"
-                        scanCount == 0 -> "Start Scanning"
-                        else -> "Resume Scanning"
-                    },
-                    fontSize = 16.sp,
-                    fontWeight = FontWeight.SemiBold,
-                    color = Color.White
-                )
-            }
-
-            // Start Measurement button (when 4+ channels detected)
-            if (isLocked || detectedCount >= 4) {
-                Spacer(modifier = Modifier.height(12.dp))
-                Button(
-                    onClick = { appState.placementComplete() },
-                    modifier = Modifier
-                        .fillMaxWidth()
-                        .height(52.dp),
-                    shape = RoundedCornerShape(14.dp),
-                    colors = ButtonDefaults.buttonColors(
-                        containerColor = Color(0xFF4CAF50)
-                    )
-                ) {
-                    Icon(
-                        Icons.Filled.PlayArrow,
-                        contentDescription = null,
-                        tint = Color.White
-                    )
+                Icon(Icons.Filled.CheckCircle, contentDescription = null, tint = Color.White)
                 Spacer(modifier = Modifier.width(8.dp))
-                    Text(
-                        text = "Start Measurement",
-                        fontSize = 16.sp,
-                        fontWeight = FontWeight.Bold,
-                        color = Color.White
-                    )
-                }
+                Text("Placement Complete", fontSize = 16.sp, fontWeight = FontWeight.Bold, color = Color.White)
             }
 
             // Skip button
-            Spacer(modifier = Modifier.height(12.dp))
-            Button(
-                onClick = { appState.placementComplete() },
-                modifier = Modifier
-                    .fillMaxWidth()
-                    .height(48.dp),
-                shape = RoundedCornerShape(14.dp),
-                colors = ButtonDefaults.buttonColors(
-                    containerColor = MlSecondaryText.copy(alpha = 0.15f)
-                )
-            ) {
+            Spacer(modifier = Modifier.height(8.dp))
+            TextButton(onClick = { isContinuousMode = false; appState.placementComplete() }) {
                 Text(
                     text = "Skip",
                     fontSize = 15.sp,
@@ -1036,7 +991,7 @@ private fun computePlacementGuide(
         val lrMax = maxOf(len4, len5, 1)
         val lrSymmetry = 1.0 - kotlin.math.abs(len4 - len5).toDouble() / lrMax
 
-        if (lrSymmetry >= 0.7 || (ch4 && ch5)) {
+        if (lrSymmetry >= 0.7) {
             return PlacementGuideResult(
                 "좌우 대칭 OK! 최종 확인 중...",
                 "checkmark.circle", 60,