feat: add demo mode for testing without BLE device

Add "Demo Mode" button in device scan screen that bypasses BLE
connection and calibration. NIRS monitoring generates simulated
random data at 4Hz. Both monitoring views show DEMO badge in top bar.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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

@@ -22,6 +22,7 @@ class AppState(private val context: Context) {
     var sensorMode by mutableStateOf(SensorMode.PIEZO)
     var bladderLevel by mutableStateOf(BladderLevel())
     var isDeviceConnected by mutableStateOf(false)
+    var isDemoMode by mutableStateOf(false)
     var piezoSettings by mutableStateOf(PiezoSettings())
     var catheterCount = mutableIntStateOf(0)
 
@@ -66,11 +67,22 @@ class AppState(private val context: Context) {
     fun goHome() {
         NirsManager.instance.stopStreaming()
         NirsManager.instance.reset()
-        bleManager.disconnect()
+        if (!isDemoMode) bleManager.disconnect()
         isDeviceConnected = false
+        isDemoMode = false
         currentScreen = AppScreen.HOME
     }
 
+    fun enterDemoMode() {
+        isDemoMode = true
+        isDeviceConnected = true
+        currentScreen = if (sensorMode == SensorMode.NIRS) {
+            AppScreen.VIVAMYO_MONITORING
+        } else {
+            AppScreen.PIEZO_MONITORING
+        }
+    }
+
     fun startFromHome() {
         currentScreen = AppScreen.SENSOR_SELECT
     }

app/src/main/java/com/example/medilightv2android/ui/views/connection/DeviceScanView.kt

@@ -251,6 +251,16 @@ fun DeviceScanView(appState: AppState) {
             }
         }
 
+        // Demo mode button
+        TextButton(
+            onClick = { appState.enterDemoMode() },
+            modifier = Modifier
+                .fillMaxWidth()
+                .padding(horizontal = 24.dp)
+        ) {
+            Text("Demo Mode (No Device)", fontSize = 14.sp, color = MlSecondaryText)
+        }
+
         // Scan button
         Button(
             onClick = {

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

@@ -48,6 +48,7 @@ fun PiezoMonitoringView(appState: AppState) {
     var reconnectionState by remember { mutableStateOf(BleReconnectionState.DISCONNECTED) }
     var isAutoMeasuring by remember { mutableStateOf(false) }
 
+    val isDemoMode = appState.isDemoMode
     val urgency = appState.bladderLevel.urgency
     val batteryLvl by bleManager.batteryLevel
     val isConnected by bleManager.isConnected
@@ -179,13 +180,18 @@ fun PiezoMonitoringView(appState: AppState) {
             }
 
             // Battery
-            Text("$batteryLvl%", fontSize = 13.sp, color = MlSecondaryText)
+            if (isDemoMode) {
+                Text("DEMO", fontSize = 11.sp, fontWeight = FontWeight.Bold, color = Color.White,
+                    modifier = Modifier.clip(RoundedCornerShape(4.dp)).background(Color(0xFFFF9500)).padding(horizontal = 6.dp, vertical = 2.dp))
+            } else {
+                Text("$batteryLvl%", fontSize = 13.sp, color = MlSecondaryText)
+            }
             Spacer(modifier = Modifier.width(4.dp))
             Box(
                 modifier = Modifier
                     .size(10.dp)
                     .clip(CircleShape)
-                    .background(if (isConnected) Color.Green else Color.Red)
+                    .background(if (isDemoMode || isConnected) Color.Green else Color.Red)
             )
         }
 

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

@@ -31,10 +31,12 @@ import com.example.medilightv2android.AppState
 import com.example.medilightv2android.ble.BleManager
 import com.example.medilightv2android.managers.NirsManager
 import com.example.medilightv2android.models.NirsMcjPacket
+import com.example.medilightv2android.models.NirsOxyResult
 import com.example.medilightv2android.ui.components.BladdyIdleRiveView
 import com.example.medilightv2android.ui.components.BleDisconnectionBanner
 import com.example.medilightv2android.ui.components.BleReconnectionState
 import com.example.medilightv2android.ui.theme.*
+import kotlin.random.Random
 
 @Composable
 fun VivamyoMonitoringView(appState: AppState) {
@@ -56,6 +58,11 @@ fun VivamyoMonitoringView(appState: AppState) {
     val sampleCount by nirsManager.sampleCount
     val isFilterEnabled by nirsManager.isFilterEnabled
 
+    val isDemoMode = appState.isDemoMode
+    var demoRunnable by remember { mutableStateOf<Runnable?>(null) }
+    var demoBaseHbO2 by remember { mutableStateOf(12.0) }
+    var demoBaseHb by remember { mutableStateOf(8.0) }
+
     var mcjRetryCount = remember { mutableIntStateOf(0) }
     var mcjRetryRunnable by remember { mutableStateOf<Runnable?>(null) }
 
@@ -108,6 +115,39 @@ fun VivamyoMonitoringView(appState: AppState) {
         handler.postDelayed(initialRetry, 2000)
     }
 
+    fun startDemoStream() {
+        val tick = object : Runnable {
+            override fun run() {
+                if (!nirsManager.isStreaming.value) return
+                demoBaseHbO2 += Random.nextDouble(-0.3, 0.3)
+                demoBaseHb += Random.nextDouble(-0.2, 0.2)
+                val hbO2 = demoBaseHbO2.coerceIn(5.0, 25.0)
+                val hb = demoBaseHb.coerceIn(3.0, 15.0)
+                demoBaseHbO2 = hbO2
+                demoBaseHb = hb
+                val tHb = hbO2 + hb
+                val stO2 = if (tHb > 0) (hbO2 / tHb * 100.0) else 0.0
+
+                nirsManager.currentOxy.value = NirsOxyResult(hbO2, hb, tHb, stO2)
+                nirsManager.sampleCount.intValue++
+                nirsManager.oxyHbO2History.add(hbO2)
+                nirsManager.oxyHbHistory.add(hb)
+                if (nirsManager.oxyHbO2History.size > 240) nirsManager.oxyHbO2History.removeAt(0)
+                if (nirsManager.oxyHbHistory.size > 240) nirsManager.oxyHbHistory.removeAt(0)
+
+                handler.postDelayed(this, 250)
+            }
+        }
+        demoRunnable = tick
+        handler.post(tick)
+    }
+
+    fun stopDemoStream() {
+        demoRunnable?.let { handler.removeCallbacks(it) }
+        demoRunnable = null
+        nirsManager.stopStreaming()
+    }
+
     fun stopNirsStream() {
         // 1. Stop polling chain & clear callback first
         nirsManager.stopStreaming()
@@ -124,11 +164,16 @@ fun VivamyoMonitoringView(appState: AppState) {
         if (isToggling) return
         isToggling = true
         if (isStreaming) {
-            stopNirsStream()
+            if (isDemoMode) stopDemoStream() else stopNirsStream()
         } else {
-            bleManager.stopBatteryPolling() // Pause battery polling during streaming
-            nirsManager.startStreaming()
-            startNirsStream()
+            if (isDemoMode) {
+                nirsManager.startStreaming()
+                startDemoStream()
+            } else {
+                bleManager.stopBatteryPolling()
+                nirsManager.startStreaming()
+                startNirsStream()
+            }
         }
         handler.postDelayed({ isToggling = false }, 1000)
     }
@@ -141,7 +186,8 @@ fun VivamyoMonitoringView(appState: AppState) {
     }
 
     DisposableEffect(Unit) { onDispose {
-        if (nirsManager.isStreaming.value) stopNirsStream()
+        if (isDemoMode) { stopDemoStream() }
+        else if (nirsManager.isStreaming.value) stopNirsStream()
         else { cancelMcjRetry(); bleManager.onNirsMcjReceived = null }
     } }
 
@@ -196,9 +242,14 @@ fun VivamyoMonitoringView(appState: AppState) {
                 Text("NIRS Monitoring", fontSize = 13.sp, color = MlSecondaryText)
             }
             Spacer(modifier = Modifier.weight(1f))
-            Text("$batteryLvl%", fontSize = 13.sp, color = MlSecondaryText)
+            if (isDemoMode) {
+                Text("DEMO", fontSize = 11.sp, fontWeight = FontWeight.Bold, color = Color.White,
+                    modifier = Modifier.clip(RoundedCornerShape(4.dp)).background(Color(0xFFFF9500)).padding(horizontal = 6.dp, vertical = 2.dp))
+            } else {
+                Text("$batteryLvl%", fontSize = 13.sp, color = MlSecondaryText)
+            }
             Spacer(modifier = Modifier.width(8.dp))
-            Box(modifier = Modifier.size(10.dp).clip(CircleShape).background(if (isConnected) Color.Green else Color.Red))
+            Box(modifier = Modifier.size(10.dp).clip(CircleShape).background(if (isDemoMode || isConnected) Color.Green else Color.Red))
         }
 
         if (showDisconnectionBanner) {