fix: 状态上报闪烁修复 + 休眠按钮状态约束

- _latestStatus 改用合并策略 (prev.copy)，保留上次报告的非 null 字段，
  避免 4 个独立订阅 (Basic/Error/Motion/Device) 交替覆盖导致闪烁
- StatusBar 电量改用独立 batteryStatus StateFlow，不依赖 status?.batteryStatus
- 休眠按钮仅非站立状态 (空闲/趴下/阻尼) 可切换，站立/RL 控制时禁用

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

app/src/main/java/com/example/m20_gamepad/ui/MainScreen.kt

@@ -171,6 +171,7 @@ fun MainScreen(
         StatusBar(
             connectionState = connectionState,
             status = status,
+            batteryStatus = batteryStatus,
             pingLatencyMs = pingLatencyMs,
             wifiSignalLevel = wifiSignalLevel,
             onStatusClick = { statusPanelVisible = true },
@@ -255,11 +256,13 @@ fun MainScreen(
                     viewModel.sendLightControl(ledStatus?.front ?: 0, if (backOn) 0 else 1)
                 }
             }
-            // 休眠/唤醒
+            // 休眠/唤醒 — 仅趴下/空闲等非站立状态可切换
             val isSleeping = status?.basicStatus?.sleep == 1
+            val canSleep = motionState != ControlCommands.MOTION_STAND &&
+                    motionState != ControlCommands.MOTION_RL_CONTROL
             SleepToggleButton(
                 isSleeping = isSleeping,
-                connected = connectionState == ProtocolClient.State.CONNECTED,
+                connected = connectionState == ProtocolClient.State.CONNECTED && canSleep,
                 onToggle = { viewModel.sendSleepSettings(!isSleeping) }
             )
             // 充电/结束充电
@@ -307,6 +310,7 @@ fun MainScreen(
 private fun StatusBar(
     connectionState: ProtocolClient.State,
     status: com.example.m20_gamepad.network.models.StatusReport?,
+    batteryStatus: com.example.m20_gamepad.network.models.BatteryStatus?,
     pingLatencyMs: Long?,
     wifiSignalLevel: Int,
     onStatusClick: () -> Unit,
@@ -340,7 +344,7 @@ private fun StatusBar(
             verticalAlignment = Alignment.CenterVertically,
             horizontalArrangement = Arrangement.spacedBy(16.dp)
         ) {
-            status?.batteryStatus?.let {
+            batteryStatus?.let {
                 val avgLevel = (it.batteryLevelLeft + it.batteryLevelRight) / 2
                 StatusChip("电量 ${avgLevel.toInt()}%")
             }

app/src/main/java/com/example/m20_gamepad/ui/MainViewModel.kt

@@ -229,7 +229,30 @@ class MainViewModel(
 
     /** 状态上报分发：更新机器人运动状态机 + 各分项缓存。 */
     private fun handleStatusReport(report: StatusReport) {
-        _latestStatus.value = report
+        // 合并：保留上次报告中非 null 的字段，避免部分报告覆盖导致 UI 闪烁
+        val prev = _latestStatus.value
+        _latestStatus.value = if (prev != null) {
+            prev.copy(
+                type = report.type,
+                command = report.command,
+                time = report.time,
+                errorCode = report.errorCode ?: prev.errorCode,
+                errorMessage = report.errorMessage ?: prev.errorMessage,
+                basicStatus = report.basicStatus ?: prev.basicStatus,
+                motionStatus = report.motionStatus ?: prev.motionStatus,
+                motorStatus = report.motorStatus ?: prev.motorStatus,
+                batteryList = report.batteryList ?: prev.batteryList,
+                batteryStatus = report.batteryStatus ?: prev.batteryStatus,
+                deviceTemperature = report.deviceTemperature ?: prev.deviceTemperature,
+                led = report.led ?: prev.led,
+                gps = report.gps ?: prev.gps,
+                devEnable = report.devEnable ?: prev.devEnable,
+                cpu = report.cpu ?: prev.cpu,
+                errorList = report.errorList ?: prev.errorList
+            )
+        } else {
+            report
+        }
         _lastUpdate.value = report.time
         robot.updateFromReport(report)
         report.errorList?.let { _errorList.value = it }