feat(dev): dev-mode RSSI live overlay · PiezoMonitoringView 도넛차트 위

BleManager:
- val rssi: MutableStateOf<Int?> — 미연결 시 null
- startRssiPolling() / stopRssiPolling() — 2초 주기 readRemoteRssi()
- Service ready 3 경로에 startRssiPolling() wire
- disconnect · gatt error · reconnect · forceDisconnect 5 경로에
  stopRssiPolling() + rssi.value = null

PiezoMonitoringView:
- val liveRssi by bleManager.rssi
- Donut 위에 dev-mode gate overlay (badge chip):
  · null → "-- dBm" gray
  · >= -60 dBm → green (strong)
  · >= -75 dBm → amber (ok)
  · <  -75 dBm → red (weak)
- 개발자모드 (3-tap Bladdy) 진입 시에만 표시

일반 사용자 UI 영향 없음 (isDevMode=false 기본).

app/src/main/java/com/medithings/vesiscan/ble/BleManager.kt

@@ -64,6 +64,8 @@ class BleManager private constructor(private val context: Context) {
     private val BATTERY_POLL_INTERVAL_MS = 30_000L     // 정상 polling 간격
     private val BATTERY_RETRY_DELAY_MS = 3_000L        // 첫 응답 재시도 지연
     private val BATTERY_RETRY_MAX = 2                  // 최대 재시도 횟수
+    private var rssiTimer: Runnable? = null
+    private val RSSI_POLL_INTERVAL_MS = 2_000L         // dev-mode UI polling 간격
     private var connectionTimer: Runnable? = null
     private var isUserDisconnect = false
     var lastConnectedAddress: String? = null
@@ -112,6 +114,8 @@ class BleManager private constructor(private val context: Context) {
         }
 
     val batteryLevel = mutableStateOf(0)
+    /** 현재 연결된 디바이스 RSSI (dBm) · 미측정/미연결 시 null. dev-mode UI 오버레이용. */
+    val rssi = mutableStateOf<Int?>(null)
     val bluetoothEnabled = mutableStateOf(bluetoothAdapter?.isEnabled == true)
     val isServiceReady = mutableStateOf(false)
 
@@ -364,6 +368,8 @@ class BleManager private constructor(private val context: Context) {
         cancelAutoReconnect()
         stopWatchdog()
         stopBatteryPolling()
+        stopRssiPolling()
+        rssi.value = null
         com.medithings.vesiscan.services.BleForegroundService.stop(context)
         connectionTimer?.let { handler.removeCallbacks(it) }
         connectionTimer = null
@@ -733,6 +739,29 @@ class BleManager private constructor(private val context: Context) {
         batteryRetryTimer = null
     }
 
+    /**
+     * RSSI polling — 2 초 주기로 `readRemoteRssi()` 요청 → `onReadRemoteRssi` 콜백이
+     * `rssi.value` 업데이트. dev-mode UI 오버레이가 이를 관찰한다.
+     * 실패해도 필수기능 영향 없음 (UC-05).
+     */
+    fun startRssiPolling() {
+        stopRssiPolling()
+        val pollRunnable = object : Runnable {
+            override fun run() {
+                if (!isConnected.value) return
+                try { bluetoothGatt?.readRemoteRssi() } catch (_: Exception) {}
+                handler.postDelayed(this, RSSI_POLL_INTERVAL_MS)
+            }
+        }
+        rssiTimer = pollRunnable
+        handler.post(pollRunnable)
+    }
+
+    fun stopRssiPolling() {
+        rssiTimer?.let { handler.removeCallbacks(it) }
+        rssiTimer = null
+    }
+
     // ── Watchdog (zombie connection detection, runs on separate thread) ──
 
     private var watchdogJob: Thread? = null
@@ -780,6 +809,8 @@ class BleManager private constructor(private val context: Context) {
                     mtbTimeoutRunnable?.let { handler.removeCallbacks(it); mtbTimeoutRunnable = null }
                         cccdRetryTimer?.let { handler.removeCallbacks(it); cccdRetryTimer = null }
                         stopBatteryPolling()
+                        stopRssiPolling()
+                        rssi.value = null
                         isConnected.value = false
                         isServiceReady.value = false
                         connectedDeviceName.value = ""
@@ -800,6 +831,8 @@ class BleManager private constructor(private val context: Context) {
 
     fun forceDisconnectAndReconnect() {
         stopBatteryPolling()
+        stopRssiPolling()
+        rssi.value = null
         stopWatchdog()
         isConnected.value = false
         isServiceReady.value = false
@@ -937,6 +970,8 @@ class BleManager private constructor(private val context: Context) {
                     debugLogger.error("GATT_ERROR status=$status newState=$newState wasConnected=$wasConnected")
 
                     stopBatteryPolling()
+                    stopRssiPolling()
+                    rssi.value = null
                     stopWatchdog()
                     // 2026-07-07 fix: 연결 실패 시 대기 중인 timer 취소.
                     fwFallbackTimer?.let { handler.removeCallbacks(it); fwFallbackTimer = null }
@@ -1011,6 +1046,8 @@ class BleManager private constructor(private val context: Context) {
                         logd { "Disconnected from ${gatt.device.address}" }
                         isConnecting.value = false
                         stopBatteryPolling()
+                        stopRssiPolling()
+                        rssi.value = null
                         // 2026-07-07 fix: disconnect 시 대기 중인 timer 취소.
                         fwFallbackTimer?.let { handler.removeCallbacks(it); fwFallbackTimer = null }
                     mtbTimeoutRunnable?.let { handler.removeCallbacks(it); mtbTimeoutRunnable = null }
@@ -1085,6 +1122,7 @@ class BleManager private constructor(private val context: Context) {
                             isServiceReady.value = true
                             onConnectionStateChanged?.invoke(true)
                             startBatteryPolling()
+                            startRssiPolling()
                             startWatchdog()
                             logd { "Service ready (no CCCD)" }
                         }
@@ -1096,6 +1134,7 @@ class BleManager private constructor(private val context: Context) {
                         isServiceReady.value = true
                         onConnectionStateChanged?.invoke(true)
                         startBatteryPolling()
+                        startRssiPolling()
                         startWatchdog()
                         logd { "Service ready (no RX)" }
                     }
@@ -1124,6 +1163,7 @@ class BleManager private constructor(private val context: Context) {
                             com.medithings.vesiscan.services.AdcCsvLogger.newSession()
                             com.medithings.vesiscan.services.BleForegroundService.start(context)
                             startBatteryPolling()
+                            startRssiPolling()
                             startWatchdog()
                             sendDeviceInfoQuery()
                             // 4초 후에도 펌웨어 미수신이면 mfv? fallback (구 펌웨어는 mid? 미지원 가능성).
@@ -1196,7 +1236,10 @@ class BleManager private constructor(private val context: Context) {
 
         override fun onReadRemoteRssi(gatt: BluetoothGatt, rssi: Int, status: Int) {
             if (status == BluetoothGatt.GATT_SUCCESS) {
-                handler.post { debugLogger.rssi(rssi) }
+                handler.post {
+                    debugLogger.rssi(rssi)
+                    this@BleManager.rssi.value = rssi
+                }
             }
         }
     }