fix: Placement GREEN CV 기준 strict화

- DEFAULT_CV_THR: 0.10 → 0.08
- 완화: 0.05/8회 → 0.03/10회 (max 0.14)
- 초기 0.08, 10회 후 0.11, 20회 후 0.14

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

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

@@ -908,7 +908,7 @@ data class PlacementGuideResult(
     val nextPhase: PlacementPhase = PlacementPhase.VERTICAL
 )
 
-private const val DEFAULT_CV_THR = 0.10
+private const val DEFAULT_CV_THR = 0.08
 private const val DEFAULT_LR_DEV_THR = 0.25
 
 /**
@@ -1104,8 +1104,8 @@ private fun computePlacementGuide(
     val std = kotlin.math.sqrt(depths.map { (it - mean) * (it - mean) }.average())
     val cv = if (mean > 0) std / mean else Double.MAX_VALUE
 
-    val relaxStep = (repeatCount / 8).coerceAtMost(2)
-    val cvThr = DEFAULT_CV_THR + relaxStep * 0.05
+    val relaxStep = (repeatCount / 10).coerceAtMost(2)
+    val cvThr = DEFAULT_CV_THR + relaxStep * 0.03
 
     // LR deviation
     var lrDev = Double.NaN