fix: BLE 로그 Downloads 폴더에 저장 (파일 탐색기 접근 가능)

- exportToDownloads(): Downloads/VesiScan_BLE_날짜.log 로 저장
- 실패 시 fallback으로 내부 저장소에 저장
- Toast로 저장 경로 안내

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

app/src/main/java/com/example/medilightv2android/services/BleDebugLogger.kt

@@ -207,11 +207,7 @@ class BleDebugLogger private constructor(private val context: Context) {
 
     // ── File Export ──
 
-    fun exportToFile(): File {
-        val fileName = "ble_debug_${dateFmt.format(Date())}.log"
-        val file = File(logDir, fileName)
-
-        file.bufferedWriter().use { writer ->
+    private fun writeLogContent(writer: java.io.BufferedWriter) {
         writer.write("=== VesiScan BLE Debug Log ===\n")
         writer.write("Device: $deviceName\n")
         writer.write("Session: ${dateFmt.format(Date(sessionStart))}\n")
@@ -230,9 +226,28 @@ class BleDebugLogger private constructor(private val context: Context) {
         }
     }
 
+    fun exportToFile(): File {
+        val fileName = "ble_debug_${dateFmt.format(Date())}.log"
+        val file = File(logDir, fileName)
+        file.bufferedWriter().use { writeLogContent(it) }
         return file
     }
 
+    /** Downloads 폴더에 저장 (파일 탐색기에서 바로 접근 가능) */
+    fun exportToDownloads(): File? {
+        return try {
+            val downloadsDir = android.os.Environment.getExternalStoragePublicDirectory(
+                android.os.Environment.DIRECTORY_DOWNLOADS
+            )
+            val fileName = "VesiScan_BLE_${dateFmt.format(Date())}.log"
+            val file = File(downloadsDir, fileName)
+            file.bufferedWriter().use { writeLogContent(it) }
+            file
+        } catch (e: Exception) {
+            null
+        }
+    }
+
     fun exportToJsonFile(): File {
         val fileName = "ble_debug_${dateFmt.format(Date())}.jsonl"
         val file = File(logDir, fileName)

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

@@ -1115,11 +1115,16 @@ private fun BleDebugPanel(bleManager: BleManager) {
                     Icon(Icons.Default.ContentCopy, "Copy", tint = Color.Gray, modifier = Modifier.size(16.dp))
                 }
 
-                // Export file button
+                // Export to Downloads
                 IconButton(
                     onClick = {
-                        val file = logger.exportToFile()
-                        android.widget.Toast.makeText(context, "Saved: ${file.name}", android.widget.Toast.LENGTH_SHORT).show()
+                        val file = logger.exportToDownloads()
+                        if (file != null) {
+                            android.widget.Toast.makeText(context, "Downloads/${file.name} 저장 완료", android.widget.Toast.LENGTH_LONG).show()
+                        } else {
+                            logger.exportToFile()
+                            android.widget.Toast.makeText(context, "내부 저장소에 저장됨", android.widget.Toast.LENGTH_SHORT).show()
+                        }
                     },
                     modifier = Modifier.size(32.dp)
                 ) {