fix: 후면반사 오판방지 수정 + 1채널 구 BV 추가

BackReflection.kt (Python 동기화):
- consensusIdx: min_votes=3 (후보 3개 미만이면 None)
- buildCandidate: post≈global_br이면 None 반환 (post를 BR로 판단 안함)
- isSuspiciousPostPeak: post>ant → post>ant×1.5 (amp_ratio=1.5)
- isReflectionOnlyMultichannel: post>ant → post>ant×1.5

BV Estimation:
- 1채널 구(sphere) 계산 추가 (Python _single_channel_bv)
  - V = (4/3)πR³, R = D/2 (cos 보정)
  - centerWallCount >= 1이면 BV 계산 (기존 3 → 1)

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

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

@@ -99,16 +99,18 @@ object BackReflection {
 
     fun buildCandidate(tgcSg: DoubleArray, postIdx: Int, postMaxIdx: Int, postMatchTol: Int = POST_MATCH_TOL): Int? {
         val globalBr = findBackReflectionIdx(tgcSg, postMaxIdx)
-        if (abs(globalBr - postIdx) <= postMatchTol) return postIdx
+        if (abs(globalBr - postIdx) <= postMatchTol) return null  // 후위벽≈전체BR → 별도 BR 없음
         return findBackReflectionAfterPost(tgcSg, postIdx, postMaxIdx)
     }
 
     // ── consensus_back_reflection_idx ──
 
-    fun consensusIdx(candidates: List<Int?>, outlierTol: Int = OUTLIER_TOL): Int? {
+    private const val MIN_VOTES = 3
+    private const val AMP_RATIO = 1.5
+
+    fun consensusIdx(candidates: List<Int?>, outlierTol: Int = OUTLIER_TOL, minVotes: Int = MIN_VOTES): Int? {
         val vals = candidates.filterNotNull()
-        if (vals.isEmpty()) return null
+        if (vals.size < minVotes) return null
-        if (vals.size == 1) return vals[0]
         val sorted = vals.sorted()
         val med = sorted[sorted.size / 2].toDouble()
         val inliers = vals.filter { abs(it - med) <= outlierTol }
@@ -119,11 +121,11 @@ object BackReflection {
 
     // ── is_suspicious_post_peak ──
 
-    fun isSuspiciousPostPeak(tgcSg: DoubleArray, postIdx: Int, antIdx: Int? = null, sharedIdx: Int? = null, sharedTol: Int = 2): Boolean {
+    fun isSuspiciousPostPeak(tgcSg: DoubleArray, postIdx: Int, antIdx: Int? = null, sharedIdx: Int? = null, sharedTol: Int = 2, ampRatio: Double = AMP_RATIO): Boolean {
         val n = tgcSg.size
         if (postIdx < 0 || postIdx >= n) return false
         var suspicious = false
-        if (antIdx != null && antIdx in 0 until n && tgcSg[postIdx] > tgcSg[antIdx]) suspicious = true
+        if (antIdx != null && antIdx in 0 until n && tgcSg[postIdx] > tgcSg[antIdx] * ampRatio) suspicious = true
         if (sharedIdx != null && abs(postIdx - sharedIdx) <= sharedTol) suspicious = true
         return suspicious
     }
@@ -171,13 +173,15 @@ object BackReflection {
         wallPairs: List<Pair<Int?, Int?>>,
         sharedIdx: Int? = null,
         sharedTol: Int = SHARED_TOL,
-        minChannels: Int = MIN_CHANNELS
+        minChannels: Int = MIN_CHANNELS,
+        ampRatio: Double = AMP_RATIO
     ): Boolean {
         data class Valid(val i: Int, val ant: Int, val post: Int)
         val valid = wallPairs.mapIndexedNotNull { i, (ant, post) ->
             if (ant != null && post != null) Valid(i, ant, post) else null
         }
         if (valid.size < minChannels) return false
+        val ratio = ampRatio
 
         // 조건 A: shared_idx 기반
         var effectiveShared = sharedIdx
@@ -188,7 +192,7 @@ object BackReflection {
             if (inliers.size >= minChannels) effectiveShared = med.roundToInt()
         }
         if (effectiveShared != null) {
-            if (valid.all { abs(it.post - effectiveShared!!) <= sharedTol && tgcSignals[it.i][it.post] > tgcSignals[it.i][it.ant] }) return true
+            if (valid.all { abs(it.post - effectiveShared!!) <= sharedTol && tgcSignals[it.i][it.post] > tgcSignals[it.i][it.ant] * ratio }) return true
         }
 
         // 조건 B: post 클러스터
@@ -196,7 +200,7 @@ object BackReflection {
         val medPost = postVals[postVals.size / 2].toDouble()
         val inlierTriples = valid.filter { abs(it.post - medPost) <= sharedTol }
         if (inlierTriples.size >= minChannels) {
-            if (inlierTriples.all { tgcSignals[it.i][it.post] > tgcSignals[it.i][it.ant] }) return true
+            if (inlierTriples.all { tgcSignals[it.i][it.post] > tgcSignals[it.i][it.ant] * ratio }) return true
         }
         return false
     }

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

@@ -447,7 +447,31 @@ fun estimateBladderVolume(
         dPost.add(dFar)
     }
 
-    if (validChannels.size < 2) return null
+    // 1채널 케이스: 구(sphere) 부피 (Python _single_channel_bv)
+    if (validChannels.size < 2) {
+        if (validChannels.size == 1) {
+            val ch = validChannels[0]
+            val theta = degreeDeg[ch] * Math.PI / 180.0
+            val dRaw = dPost[0] - dAnt[0]
+            val D = if (applyAngleCorrection) dRaw * cos(theta) else dRaw
+            val R = D / 2.0
+            val bvMm3 = (4.0 / 3.0) * Math.PI * R * R * R
+            val S = areaK * D * D * lrRatio
+            val yMid = sensorZMm[ch] + (dAnt[0] + dPost[0]) / 2.0 * sin(theta)
+            return BVResult(
+                volumeMl = bvMm3 / 1000.0, volumeMm3 = bvMm3,
+                validChannels = validChannels, dAntMm = dAnt.toDoubleArray(), dPostMm = dPost.toDoubleArray(),
+                dMm = doubleArrayOf(D), sMm2 = doubleArrayOf(S),
+                sortedChannels = listOf(ch), sortedYMm = doubleArrayOf(yMid), sortedSMm2 = doubleArrayOf(S),
+                vFrustumMm3 = doubleArrayOf(), vCoreMm3 = 0.0,
+                vBottomMm3 = bvMm3, vTopMm3 = 0.0,
+                bottomHMm = R, topHMm = 0.0,
+                bottomKind = "sphere", topKind = "sphere",
+                lrRatio = lrRatio, distancePerSample = distancePerSample, delayOffsetMm = delayOffsetMm
+            )
+        }
+        return null
+    }
     val n = validChannels.size
 
     // theta, sensor_z for valid channels

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

@@ -229,21 +229,22 @@ fun PiezoMonitoringView(appState: AppState) {
                             (0..5).map { allWalls[it]?.let { w -> w.second - w.first } ?: 0 })
                         logService.logMeasurement(methodCBvMl, channelLogs, rawADC)
                         com.example.medilightv2android.services.AdcCsvLogger.log(rawADC, methodCBvMl)
-                    } else if (centerWallCount >= 3) {
+                    } else if (centerWallCount >= 1) {
                         val bvResult = estimateBladderVolume6ch(allWalls)
                         if (bvResult != null) {
                             rawVolumeMl = bvResult.volumeMl
                             rawLrRatio = bvResult.lrRatio
-                            Log.d("PiezoMonitor", "BV[$methodLabel]: ${"%.1f".format(bvResult.volumeMl)}ml (6ch, lr=${"%.2f".format(bvResult.lrRatio)}, center=${centerWallCount}/4)")
+                            val mode = if (centerWallCount == 1) "sphere" else "frustum"
+                            Log.d("PiezoMonitor", "BV[$methodLabel]: ${"%.1f".format(bvResult.volumeMl)}ml ($mode, lr=${"%.2f".format(bvResult.lrRatio)}, center=${centerWallCount}/4)")
                             bleManager.debugLogger.measurementResult(bvResult.volumeMl, bvResult.lrRatio, totalWallCount,
                                 (0..5).map { allWalls[it]?.let { w -> w.second - w.first } ?: 0 },
                                 otsuThreshold = analyzer.lastOtsuThreshold)
                             logService.logMeasurement(bvResult.volumeMl, channelLogs, rawADC)
                             com.example.medilightv2android.services.AdcCsvLogger.log(rawADC, bvResult.volumeMl, bvResult.lrRatio)
                         }
-                    } else if (centerWallCount > 0) {
+                    } else if (totalWallCount > 0) {
-                        Log.w("PiezoMonitor", "Insufficient center channels: $centerWallCount/4 (need 3+)")
+                        Log.w("PiezoMonitor", "No center channels: center=0 total=$totalWallCount/6")
-                        bleManager.debugLogger.warn("BV_SKIP scan=${com.example.medilightv2android.services.AdcCsvLogger.lastScanId} center=$centerWallCount/4 total=$totalWallCount/6")
+                        bleManager.debugLogger.warn("BV_SKIP scan=${com.example.medilightv2android.services.AdcCsvLogger.lastScanId} center=0 total=$totalWallCount/6")
                         com.example.medilightv2android.services.AdcCsvLogger.log(rawADC, null)
                         if (!isAutoMeasuring) {
                             handler.post { android.widget.Toast.makeText(context,