fix: Piezo 진입 시 bladderLevel 0으로 초기화 (이전 세션 값 잔류 방지)

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

app/src/main/java/com/example/medilightv2android/AppState.kt

@@ -125,6 +125,8 @@ class AppState(private val context: Context) {
     }
 
     fun placementComplete() {
+        bladderLevel = BladderLevel(currentLevel = 0, catheterizationThreshold = bladderLevel.catheterizationThreshold)
+        storage.bladderLevel = 0
         currentScreen = AppScreen.PIEZO_MONITORING
     }