feat: add Piezo BLE data pipeline (1:1 port from iOS)

PiezoPacketCollector.kt:
- Multi-packet reb:/red:/raa: assembly
- Auto-detect Big/Little Endian
- First channel locks endianness for all channels
- 6-channel support (maa command)

BleManager.kt:
- sendAllChannels(mode) → maa command
- reb:/rer:/raa: response routing to piezoCollector
- piezoCollector instance added

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

app/src/main/java/com/example/medilightv2android/ble/BleManager.kt

@@ -274,7 +274,9 @@ class BleManager private constructor(private val context: Context) {
     }
 
     // Piezo Commands
-    fun sendPiezoPowerOn(freqOption: Int, cycles: Int) {
+    val piezoCollector = PiezoPacketCollector()
+
+    fun sendPiezoPowerOn(freqOption: Int = 2, cycles: Int = 5) {
         sendRaw(CRC16.buildCommand("mpa", intArrayOf(freqOption, cycles)))
     }
 
@@ -286,6 +288,12 @@ class BleManager private constructor(private val context: Context) {
         sendRaw(CRC16.buildCommand("mec", intArrayOf(freqOption, delayUs, 140, cycles, 1, piezoCh)))
     }
 
+    /** 6-channel measurement (maa) */
+    fun sendAllChannels(mode: Int = 0) {
+        piezoCollector.startMultiChannel(6)
+        sendRaw(CRC16.buildCommand("maa", intArrayOf(mode)))
+    }
+
     // NIRS Commands
     fun sendNirsPowerOn() {
         sendRaw(CRC16.buildCommand("mta", intArrayOf(1)))
@@ -505,6 +513,14 @@ class BleManager private constructor(private val context: Context) {
             "rag:", "rag!" -> onNirsMagReceived?.invoke(data)
             "rcj:", "rcj!" -> onNirsMcjReceived?.invoke(data)
             "rpa:" -> onPiezoDataReceived?.invoke(data)
+            // Piezo echo responses → route to packet collector
+            "rer:" -> {
+                // VesiScan-Basic preliminary header — just acknowledge, reb: follows
+                logd { "rer: preliminary header (${data.size} bytes)" }
+            }
+            "reb:" -> piezoCollector.addPacket(data)
+            "red:" -> piezoCollector.addPacket(data)
+            "ree:", "raa:" -> piezoCollector.addPacket(data)
             "rsn:" -> {
                 if (data.size >= 6) {
                     val millivolts = ((data[4].toInt() and 0xFF) shl 8) or (data[5].toInt() and 0xFF)