feat: Otsu adaptive threshold, Method A 포팅, BV ellipse cap, UI 정리

Algorithm:
- Otsu 1D adaptive threshold 포팅 (span_utils.py otsu_1d, 기본 ON)
- Method A 벽 검출 포팅 (PiezoEchoAnalyzerA.kt: plateau score + prominence)
- Method A cross-validation (채널간 중앙값/gradient 보정)
- BV cap 높이: parabolic → ellipse 피팅 (8점 축정렬 타원)
- Bottom cap: sphere, Top cap: cone (Python bv_estimation.py 동기화)
- 설정에 Method A/B 토글 (왼쪽=A, 오른쪽=B)

Logging:
- BLE 로그 + CSV에 otsu threshold 값 기록
- 측정 로그에 method label (A/B) 표시

UI:
- 설정 패널: floating overlay로 변경 + MaxVolume 슬라이더 추가
- Onboarding: 1페이지로 단순화 (Pager/indicator 제거)
- Registration: 한 페이지에 전체 입력 + Skip 버튼
- Placement: 로딩 인디케이터/스캔 텍스트 삭제

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

app/src/main/java/com/example/medilightv2android/services/BleDebugLogger.kt

@@ -155,7 +155,7 @@ class BleDebugLogger private constructor(private val context: Context) {
         info("ENDIAN_DETECT ${if (isBigEndian) "BIG" else "LITTLE"} (LE=$firstSampleLE, BE=$firstSampleBE)")
     }
 
-    fun measurementResult(volumeMl: Double?, lrRatio: Double, validChannels: Int, urineLines: List<Int>) {
+    fun measurementResult(volumeMl: Double?, lrRatio: Double, validChannels: Int, urineLines: List<Int>, otsuThreshold: Double = 0.0) {
         val scanId = AdcCsvLogger.lastScanId
         val msg = buildString {
             append("MEASUREMENT scan=$scanId")
@@ -163,6 +163,7 @@ class BleDebugLogger private constructor(private val context: Context) {
             append(" lr=${"%.2f".format(lrRatio)}")
             append(" valid=$validChannels/6")
             append(" urine=[${urineLines.joinToString(",")}]")
+            if (otsuThreshold > 0) append(" otsu=${"%.0f".format(otsuThreshold)}")
         }
         add(Entry(System.currentTimeMillis(), Level.INFO, msg))
     }