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/qr/qr.go

@@ -0,0 +1,108 @@
+// Package qr handles otpauth:// QR-code parsing. Image decoding is done
+// with gozxing (pure Go, no CGO); URL parsing is hand-rolled per the
+// otpauth:// spec used by Google Authenticator, Authy, and friends.
+//
+// https://github.com/google/google-authenticator/wiki/Key-Uri-Format
+package qr
+
+import (
+	"errors"
+	"fmt"
+	"image"
+	"net/url"
+	"strconv"
+	"strings"
+
+	"github.com/makiuchi-d/gozxing"
+	"github.com/makiuchi-d/gozxing/qrcode"
+)
+
+// ErrNoQR is returned when the image does not contain a decodable QR code.
+var ErrNoQR = errors.New("qr: no QR code found in image")
+
+// ErrNotOtpAuth is returned when the QR decodes successfully but does
+// not contain an otpauth:// URI.
+var ErrNotOtpAuth = errors.New("qr: decoded text is not an otpauth:// URI")
+
+// DecodeImage runs the gozxing QR reader on img and returns the decoded
+// text. Returns ErrNoQR if no QR pattern was found.
+func DecodeImage(img image.Image) (string, error) {
+	bmp, err := gozxing.NewBinaryBitmapFromImage(img)
+	if err != nil {
+		return "", fmt.Errorf("qr: bitmap: %w", err)
+	}
+	reader := qrcode.NewQRCodeReader()
+	result, err := reader.Decode(bmp, nil)
+	if err != nil {
+		return "", ErrNoQR
+	}
+	return result.GetText(), nil
+}
+
+// OtpAuth carries the parsed pieces of an otpauth:// URI in the form
+// the UI needs to create a config.Entry.
+type OtpAuth struct {
+	// Type is "totp" or "hotp".
+	Type string
+	// Label is the human-readable display name (issuer + ":" + account).
+	Label string
+	// SecretBase32 is the Base32-encoded HMAC secret.
+	SecretBase32 string
+	// Issuer is the optional issuer string ("Google", "GitHub", ...).
+	Issuer string
+	// Algorithm is "SHA1", "SHA256", or "SHA512". Empty = unspecified.
+	Algorithm string
+	// Digits is the OTP length (typically 6). 0 = unspecified.
+	Digits int
+	// Period is the TOTP step in seconds (typically 30). 0 = unspecified.
+	Period int
+	// Counter is the HOTP initial counter.
+	Counter uint64
+}
+
+// ParseOtpAuth turns an otpauth:// URI into an OtpAuth struct. The
+// secret is left base32-encoded; callers feed it straight into the
+// authenticator's Enroll method.
+func ParseOtpAuth(raw string) (*OtpAuth, error) {
+	const fn = "internal.qr.ParseOtpAuth"
+	raw = strings.TrimSpace(raw)
+	if !strings.HasPrefix(strings.ToLower(raw), "otpauth://") {
+		return nil, ErrNotOtpAuth
+	}
+	u, err := url.Parse(raw)
+	if err != nil {
+		return nil, fmt.Errorf("%s: parse URL: %w", fn, err)
+	}
+	typ := strings.ToLower(u.Host)
+	if typ != "totp" && typ != "hotp" {
+		return nil, fmt.Errorf("%s: unsupported otpauth type %q", fn, typ)
+	}
+	q := u.Query()
+	secret := strings.TrimSpace(q.Get("secret"))
+	if secret == "" {
+		return nil, fmt.Errorf("%s: missing secret", fn)
+	}
+	out := &OtpAuth{
+		Type:         typ,
+		Label:        strings.TrimPrefix(u.Path, "/"),
+		SecretBase32: secret,
+		Issuer:       q.Get("issuer"),
+		Algorithm:    strings.ToUpper(q.Get("algorithm")),
+	}
+	if v := q.Get("digits"); v != "" {
+		if n, err := strconv.Atoi(v); err == nil {
+			out.Digits = n
+		}
+	}
+	if v := q.Get("period"); v != "" {
+		if n, err := strconv.Atoi(v); err == nil {
+			out.Period = n
+		}
+	}
+	if v := q.Get("counter"); v != "" {
+		if n, err := strconv.ParseUint(v, 10, 64); err == nil {
+			out.Counter = n
+		}
+	}
+	return out, nil
+}