feat(sdk): 重命名 owner→brand 并在硬绑前校验设备品牌

- DuooomiBleConfig.owner → brand（语义：设备品牌名），HTTP header x-owner 不变
- bind() 前置 verifyBrand：缺 deviceInfo 先 getDeviceInfo，与 config.brand 严格匹配，不一致主动断连并抛 .brandMismatch
- README 抹除软绑/对账/UpgradeRecord 等内部实现细节，仅保留厂商面向的公开 API（功能代码完全保留）

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

Sources/DuooomiBleSDK/Services/FirmwareUpgradeService.swift

@@ -89,7 +89,7 @@ final class FirmwareUpgradeService {
         req.setValue("application/json", forHTTPHeaderField: "Content-Type")
         req.setValue("application/json", forHTTPHeaderField: "Accept")
         req.setValue(config.apiKey, forHTTPHeaderField: "x-api-key")
-        req.setValue(config.owner, forHTTPHeaderField: "x-owner")
+        req.setValue(config.brand, forHTTPHeaderField: "x-owner")
         do {
             req.httpBody = try JSONEncoder().encode(body)
         } catch {