feat(sdk): OTA 升级流程对齐 expo + 拆 extension 文件分层 + 秘钥本地化

主要改动：
- 新增 fetchLatestFirmware/upgradeFirmware/tryReportPendingUpgrade
  三段 OTA 接口，对齐 expo bindDeviceWithOrchestration 行为
- bind 仅做硬绑+getVersion，软绑/对账上报/拉最新固件搬到
  fetchLatestFirmware 内部串；软绑失败自动硬解回滚
- UpgradeRecord 复合主键 (sn, firmwareId) 持久化 + sn 级 in-flight 互斥
- DuooomiBleSDKDelegate 新增 didUpdateUpgradeRecords，集成方
  可观察对账上报结果（reported/outcome 状态）
- DuooomiBleSDK 主类按职责拆 5 个 extension 文件，公开 API 不变
- TargetFirmware 简化为只取必要字段 + 新增 forceUpgrade
- scanNamePrefix 改为必填 String
- demo 秘钥移至本地 DemoSecrets.swift (gitignored)
- README 重写：完整 OTA 流程示例 + 上报状态判定表

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

demo/Sources/DemoApp.swift

@@ -16,8 +16,21 @@ struct DemoApp: App {
 }
 
 /// ViewModel 包装 SDK callback API，通过 DuooomiBleSDKDelegate 驱动 UI 更新。
-class DemoViewModel: NSObject, ObservableObject, DuooomiBleSDKDelegate {
-    let sdk: DuooomiBleSDK
+final class DemoViewModel: NSObject, ObservableObject, DuooomiBleSDKDelegate {
+
+    // MARK: - SDK Config（demo 内可改，持久化到 UserDefaults）
+
+    @Published var configOwner: String {
+        didSet { defaults.set(configOwner, forKey: Self.keyOwner) }
+    }
+    @Published var configApiKey: String {
+        didSet { defaults.set(configApiKey, forKey: Self.keyApiKey) }
+    }
+    @Published var configScanPrefix: String {
+        didSet { defaults.set(configScanPrefix, forKey: Self.keyScanPrefix) }
+    }
+
+    // MARK: - SDK State (driven by delegate)
 
     @Published var btState: ConnectionState = .idle
     @Published var connectedDevice: DiscoveredDevice? = nil
@@ -27,11 +40,63 @@ class DemoViewModel: NSObject, ObservableObject, DuooomiBleSDKDelegate {
     @Published var isActivated: Bool = false
     @Published var transferProgress: Int = 0
     @Published var error: String? = nil
+    @Published var upgradeRecords: [UpgradeRecord] = []
+
+    @Published private(set) var sdk: DuooomiBleSDK
+
+    // MARK: - Internals
+
+    private let defaults = UserDefaults.standard
+    private static let keyOwner = "demo.config.owner"
+    private static let keyApiKey = "demo.config.apiKey"
+    private static let keyScanPrefix = "demo.config.scanPrefix"
+
+    /// demo 调试默认值（仅当 UserDefaults 没存过时使用）。秘钥从 DemoSecrets 读，避免泄露到仓库。
+    private static let defaultOwner = DemoSecrets.owner
+    private static let defaultApiKey = DemoSecrets.apiKey
+    private static let defaultScanPrefix = DemoSecrets.scanNamePrefix
 
     override init() {
-        sdk = DuooomiBleSDK(config: .init(apiKey: ""))
+        let d = UserDefaults.standard
+        let owner = d.string(forKey: Self.keyOwner) ?? Self.defaultOwner
+        let apiKey = d.string(forKey: Self.keyApiKey) ?? Self.defaultApiKey
+        let scanPrefix = d.string(forKey: Self.keyScanPrefix) ?? Self.defaultScanPrefix
+
+        self.configOwner = owner
+        self.configApiKey = apiKey
+        self.configScanPrefix = scanPrefix
+
+        self.sdk = DuooomiBleSDK(config: .init(
+            apiKey: apiKey,
+            owner: owner,
+            scanNamePrefix: scanPrefix
+        ))
+
         super.init()
         sdk.delegate = self
+        // 初次加载 SDK 持久化的 records（之前历史升级 / 待对账）
+        upgradeRecords = sdk.upgradeRecords
+    }
+
+    /// demo 内修改配置后调用：重新创建 SDK 实例并迁移 delegate。
+    func reloadSDK() {
+        let new = DuooomiBleSDK(config: .init(
+            apiKey: configApiKey,
+            owner: configOwner,
+            scanNamePrefix: configScanPrefix
+        ))
+        new.delegate = self
+        self.sdk = new
+        // 重置展示状态
+        btState = .idle
+        connectedDevice = nil
+        discoveredDevices = []
+        deviceInfo = nil
+        version = ""
+        isActivated = false
+        transferProgress = 0
+        error = nil
+        upgradeRecords = new.upgradeRecords
     }
 
     // MARK: - DuooomiBleSDKDelegate
@@ -64,6 +129,10 @@ class DemoViewModel: NSObject, ObservableObject, DuooomiBleSDKDelegate {
         transferProgress = progress
     }
 
+    func sdk(_ sdk: DuooomiBleSDK, didUpdateUpgradeRecords records: [UpgradeRecord]) {
+        upgradeRecords = records
+    }
+
     func sdk(_ sdk: DuooomiBleSDK, didEncounterError error: String?) {
         self.error = error
     }