fix: 流程对齐 iOS 严格 1:1（disconnect 不清 sn/firmwareUpgrade）

发现并修正以下 1:1 复刻偏离：

1. SDK：disconnect 行为
   - iOS：被动断开 / 主动 disconnect 都 **不清** sn / firmwareUpgrade
     · sn 仅在 unbind 成功 / fetchLatestFirmware 软绑失败回滚时清空
     · firmwareUpgrade 仅在 fetchLatestFirmware 成功时覆盖
   - 之前 Android 在两个 disconnect 入口都清，与 iOS 不一致；现已修正

2. Demo：otaFetchUserId / otaFetchSn 进入页面时的初始化
   - iOS：onAppear 时同步默认 userId / 当前 sdk.sn 到字段
   - Android：之前 bind 后才填，进入页面默认空；现已与 iOS 对齐

3. Demo：ConfigField 禁用自动大写 / 自动纠错
   - iOS 用 .autocapitalization(.none).disableAutocorrection(true)
   - Android 加 KeyboardOptions(autoCorrect=false, capitalization=None)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

sdk/src/main/kotlin/com/duooomi/ble/DuooomiBleSDK.kt

@@ -100,11 +100,12 @@ class DuooomiBleSDK(context: Context, val config: DuooomiBleConfig) {
                 _deviceInfo.value = null
                 _version.value = ""
                 _isActivated.value = false
-                _sn.value = ""
-                _firmwareUpgrade.value = null
                 _btState.value = ConnectionState.DISCONNECTED
                 protocolService.stopListening()
                 cancelAllPending(DuooomiBleError.NotConnected)
+                // 与 iOS 一致：sn / firmwareUpgrade 不在断开时重置
+                // —— sn 仅在 unbind 成功 / fetchLatestFirmware 软绑失败回滚时清空
+                // —— firmwareUpgrade 仅在 fetchLatestFirmware 成功时覆盖
             }
         }
     }
@@ -198,8 +199,6 @@ class DuooomiBleSDK(context: Context, val config: DuooomiBleConfig) {
         _deviceInfo.value = null
         _version.value = ""
         _isActivated.value = false
-        _sn.value = ""
-        _firmwareUpgrade.value = null
         _btState.value = ConnectionState.DISCONNECTED
         BleLog.i("Disconnected", "Connect")