feat: Phase 1 WinAuth Go 移植完整实现

将原 C#/.NET WinAuth 移植为 Go + Gio GUI，覆盖 Phase 1 全部功能。

核心模块：
- internal/authenticator: TOTP (Google/Microsoft/Okta) + HOTP + BattleNet + Steam，含
  enroll/sync/code 生成、Steam 交易确认轮询
- internal/config: YAML 配置 + 老版 WinAuth XML 导入（DPAPI + Password + Blowfish/PBKDF2 解密链）
- internal/crypto: 现代加密 (WAGO1) + DPAPI 跨平台封装 + 老版 Blowfish ECB
- internal/win32: 单实例 Mutex 锁 + 全局热键管理器 (RegisterHotKey + PeekMessage 泵) +
  SendInput Unicode 注入 + 剪贴板文本/CF_DIB 图像读写 + AttachThreadInput 焦点切换
- internal/hotkey: "Ctrl+Alt+G" 风格快捷键字符串解析/格式化
- internal/qr: gozxing 二维码解码 + otpauth:// URI 解析
- internal/i18n: en/zh-CN/de 三语 TOML

UI 模块 (Gio)：
- 主窗口：圆环倒计时进度条、复制按钮 + Toast 反馈、空列表占位、行分隔线
- 添加流程：vendor 菜单 + 各 vendor 独立对话框 + 二维码扫描入口（文件 / 剪贴板）
- 设置：密码加密、老版 XML 导入、每条目热键配置
- Steam：注册向导（含 captcha/email/SMS 多步）+ 交易确认窗

构建：Windows 主目标，非 Windows 平台所有 Win32 功能走 build-tag 桩实现。

internal/ui/convert.go

@@ -0,0 +1,49 @@
+package ui
+
+import (
+	"fmt"
+
+	"git.wxccs.org/iceking2nd/winauth-go/internal/authenticator"
+	"git.wxccs.org/iceking2nd/winauth-go/internal/config"
+)
+
+// entryFromAuthenticator builds a serializable config.Entry from an
+// in-memory authenticator plus its display name. The vendor string is
+// derived from the authenticator's Name() (which already returns
+// "google" / "microsoft" / "okta" / "hotp" / "battlenet" / "steam").
+func entryFromAuthenticator(name string, a authenticator.Authenticator, hotkey string) config.Entry {
+	return config.Entry{
+		Name:      name,
+		Vendor:    a.Name(),
+		SecretRaw: a.SecretData(),
+		Hotkey:    hotkey,
+	}
+}
+
+// buildAuthenticator is the reverse of entryFromAuthenticator: it picks
+// the right concrete type based on vendor, then asks it to parse the
+// stored secret blob.
+func buildAuthenticator(e config.Entry) (authenticator.Authenticator, error) {
+	const fn = "internal.ui.buildAuthenticator"
+	var a authenticator.Authenticator
+	switch e.Vendor {
+	case "google", "":
+		a = authenticator.NewGoogleAuthenticator()
+	case "microsoft":
+		a = authenticator.NewMicrosoftAuthenticator()
+	case "okta":
+		a = authenticator.NewOktaVerifyAuthenticator()
+	case "hotp":
+		a = authenticator.NewHOTPAuthenticator()
+	case "battlenet":
+		a = authenticator.NewBattleNetAuthenticator()
+	case "steam":
+		a = authenticator.NewSteamAuthenticator()
+	default:
+		return nil, fmt.Errorf("%s: unknown vendor %q", fn, e.Vendor)
+	}
+	if err := a.SetSecretData(e.SecretRaw); err != nil {
+		return nil, fmt.Errorf("%s: decode entry %q: %w", fn, e.Name, err)
+	}
+	return a, nil
+}