Fix camera screen: navigate via AppScreen instead of overlay

Camera was hidden behind PiezoMonitoringView because it was rendered
as a child composable. Now uses AppScreen.URINE_CAMERA for full
Crossfade navigation — camera gets its own screen transition.

Flow: Catheterize → 카메라 → AppScreen.URINE_CAMERA → measure → back to PIEZO_MONITORING

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

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

@@ -14,7 +14,8 @@ enum class AppScreen {
     ONBOARDING, REGISTRATION, HOME, SENSOR_SELECT, DEVICE_SCAN,
     NIRS_CALIBRATION, PIEZO_PERSONALIZATION, PIN_SETUP, PIN_ENTRY,
     VIVAMYO_MONITORING, PIEZO_MONITORING, MEASUREMENT_HISTORY,
-    VOIDING_DIARY
+    VOIDING_DIARY,
+    URINE_CAMERA
 }
 
 class AppState(private val context: Context) {