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/config/legacy_secretdata.go

@@ -0,0 +1,35 @@
+package config
+
+import (
+	"errors"
+	"strings"
+)
+
+// normalizeLegacySecretData hands the decrypted WinAuth SecretData string
+// off to the modern Entry.SecretRaw slot. The modern authenticator
+// SetSecretData methods already accept the exact C# WinAuth on-disk form
+// (tab-separated head with pipe-separated trailers), so the conversion
+// is mostly a sanity check.
+//
+// vendor is the value detectLegacyVendor produced and is used only to
+// catch obviously empty/malformed payloads early; the per-vendor parse
+// happens later in authenticator.SetSecretData.
+func normalizeLegacySecretData(vendor, secret string) (string, error) {
+	secret = strings.TrimSpace(secret)
+	if secret == "" {
+		return "", errors.New("legacy entry: empty secret payload")
+	}
+	switch vendor {
+	case "battlenet":
+		// Either "<hex>\t...|<serialhex>" (modern C# form) or the
+		// legacy WinAuth2 short form "<40 hex secret><utf8-hex serial>".
+		// Both are accepted by BattleNetAuthenticator.SetSecretData.
+		return secret, nil
+	case "steam":
+		// "<hex>\t...|serial|device|steamdata|session" — SetSecretData
+		// also tolerates fewer fields.
+		return secret, nil
+	default:
+		return secret, nil
+	}
+}