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/i18n/i18n.go

@@ -0,0 +1,86 @@
+package i18n
+
+import (
+	"embed"
+	"fmt"
+	"strings"
+
+	"github.com/nicksnyder/go-i18n/v2/i18n"
+	"golang.org/x/text/language"
+	"gopkg.in/yaml.v3"
+
+	"git.wxccs.org/iceking2nd/winauth-go/internal/global"
+)
+
+//go:embed locales/*.toml
+var localeFS embed.FS
+
+var (
+	bundle    *i18n.Bundle
+	localizer *i18n.Localizer
+)
+
+// Init loads bundled locales and selects a localizer based on the requested
+// language tag. Pass an empty string to use the system default (currently
+// English).
+func Init(lang string) error {
+	const fn = "internal.i18n.Init"
+
+	bundle = i18n.NewBundle(language.English)
+	bundle.RegisterUnmarshalFunc("toml", tomlUnmarshal)
+	bundle.RegisterUnmarshalFunc("yaml", yaml.Unmarshal)
+
+	entries, err := localeFS.ReadDir("locales")
+	if err != nil {
+		return fmt.Errorf("read locales: %w", err)
+	}
+	for _, e := range entries {
+		if e.IsDir() {
+			continue
+		}
+		path := "locales/" + e.Name()
+		if _, err := bundle.LoadMessageFileFS(localeFS, path); err != nil {
+			global.Log.WithField("func", fn).WithError(err).
+				WithField("file", path).Warn("failed to load locale")
+		}
+	}
+
+	if strings.TrimSpace(lang) == "" {
+		lang = "en"
+	}
+	localizer = i18n.NewLocalizer(bundle, lang, "en")
+
+	global.Log.WithField("func", fn).WithField("lang", lang).Debug("i18n initialized")
+	return nil
+}
+
+// T translates the given message id using the active localizer. If
+// translation fails (missing key or i18n not initialized), it returns the
+// id unchanged so the UI still renders something readable.
+func T(id string, args ...any) string {
+	if localizer == nil {
+		return id
+	}
+	cfg := &i18n.LocalizeConfig{MessageID: id}
+	if len(args) > 0 {
+		// args are formatted directly via fmt.Sprintf if the message
+		// id contains %s/%d-style verbs.
+		out, err := localizer.Localize(cfg)
+		if err != nil {
+			return fmt.Sprintf(id, args...)
+		}
+		return fmt.Sprintf(out, args...)
+	}
+	out, err := localizer.Localize(cfg)
+	if err != nil {
+		return id
+	}
+	return out
+}
+
+// SetLanguage switches the active language at runtime.
+func SetLanguage(lang string) {
+	const fn = "internal.i18n.SetLanguage"
+	localizer = i18n.NewLocalizer(bundle, lang, "en")
+	global.Log.WithField("func", fn).WithField("lang", lang).Debug("language changed")
+}