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/crypto/legacy_blowfish.go

@@ -0,0 +1,84 @@
+package crypto
+
+import (
+	"crypto/cipher"
+	"encoding/hex"
+	"errors"
+	"fmt"
+
+	"golang.org/x/crypto/blowfish"
+)
+
+// LegacyDecryptBlowfish decrypts the hex-encoded payload produced by the
+// original WinAuth Authenticator.Decrypt(string, byte[]) method, which uses
+// CBC-less Blowfish with ISO10126-2 padding via BouncyCastle's
+// PaddedBufferedBlockCipher.
+//
+// The BouncyCastle "PaddedBufferedBlockCipher" with no IV is effectively
+// ECB; the original WinAuth code chose Blowfish in that mode and relied on
+// ISO10126-2 to round the payload to the block size.
+func LegacyDecryptBlowfish(hexCiphertext string, key []byte) ([]byte, error) {
+	ct, err := hex.DecodeString(hexCiphertext)
+	if err != nil {
+		return nil, fmt.Errorf("legacy blowfish: hex decode: %w", err)
+	}
+	cph, err := blowfish.NewCipher(key)
+	if err != nil {
+		return nil, fmt.Errorf("legacy blowfish: %w", err)
+	}
+	bs := cph.BlockSize()
+	if len(ct)%bs != 0 {
+		return nil, errors.New("legacy blowfish: ciphertext not a multiple of block size")
+	}
+	out := make([]byte, len(ct))
+	for i := 0; i < len(ct); i += bs {
+		cph.Decrypt(out[i:i+bs], ct[i:i+bs])
+	}
+	return stripISO10126(out, bs)
+}
+
+// LegacyEncryptBlowfish is provided for symmetry / round-trip tests; the
+// new format never writes Blowfish.
+func LegacyEncryptBlowfish(plaintext, key []byte) (string, error) {
+	cph, err := blowfish.NewCipher(key)
+	if err != nil {
+		return "", err
+	}
+	padded, err := padISO10126(plaintext, cph.BlockSize())
+	if err != nil {
+		return "", err
+	}
+	out := make([]byte, len(padded))
+	for i := 0; i < len(padded); i += cph.BlockSize() {
+		cph.Encrypt(out[i:i+cph.BlockSize()], padded[i:i+cph.BlockSize()])
+	}
+	return hex.EncodeToString(out), nil
+}
+
+// stripISO10126 removes ISO 10126-2 padding: last byte = pad length;
+// preceding bytes are arbitrary.
+func stripISO10126(buf []byte, blockSize int) ([]byte, error) {
+	if len(buf) == 0 {
+		return nil, errors.New("iso10126: empty buffer")
+	}
+	padLen := int(buf[len(buf)-1])
+	if padLen <= 0 || padLen > blockSize {
+		return nil, errors.New("iso10126: invalid padding length")
+	}
+	return buf[:len(buf)-padLen], nil
+}
+
+func padISO10126(buf []byte, blockSize int) ([]byte, error) {
+	padLen := blockSize - len(buf)%blockSize
+	out := make([]byte, len(buf)+padLen)
+	copy(out, buf)
+	// fill with deterministic-but-non-zero bytes so tests are reproducible
+	// (real WinAuth uses a CSPRNG; the actual content is ignored on decrypt).
+	for i := len(buf); i < len(out)-1; i++ {
+		out[i] = byte(i)
+	}
+	out[len(out)-1] = byte(padLen)
+	// silence linter for unused cipher variable if any
+	_ = cipher.NewCBCEncrypter
+	return out, nil
+}