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/crypto.go

@@ -0,0 +1,98 @@
+// Package crypto implements the password-based and DPAPI-based encryption
+// layers that the original WinAuth used to protect its config XML, plus a
+// modern AES-GCM scheme used by the new YAML/JSON config format.
+//
+// The legacy reader is provided for one-way migration only — new files are
+// always written in the modern format.
+package crypto
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"crypto/sha1"
+	"crypto/sha256"
+	"encoding/base64"
+	"errors"
+	"fmt"
+
+	"golang.org/x/crypto/pbkdf2"
+)
+
+const (
+	saltLength       = 8
+	legacyIterations = 2000
+	legacyKeySize    = 32 // 256 bits
+)
+
+// EncryptModern encrypts plaintext with a passphrase using PBKDF2-SHA256 +
+// AES-256-GCM. The wire format is:
+//
+//	"WAGO1" || base64( salt(16) || nonce(12) || ciphertext+tag )
+//
+// All-in-one base64 makes the result safe to embed in YAML/JSON.
+func EncryptModern(plaintext, passphrase []byte) (string, error) {
+	salt := make([]byte, 16)
+	if _, err := rand.Read(salt); err != nil {
+		return "", err
+	}
+	key := pbkdf2.Key(passphrase, salt, 100_000, 32, sha256.New)
+
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return "", err
+	}
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return "", err
+	}
+	nonce := make([]byte, gcm.NonceSize())
+	if _, err := rand.Read(nonce); err != nil {
+		return "", err
+	}
+	ct := gcm.Seal(nil, nonce, plaintext, nil)
+
+	buf := make([]byte, 0, len(salt)+len(nonce)+len(ct))
+	buf = append(buf, salt...)
+	buf = append(buf, nonce...)
+	buf = append(buf, ct...)
+	return "WAGO1" + base64.StdEncoding.EncodeToString(buf), nil
+}
+
+// DecryptModern is the inverse of EncryptModern.
+func DecryptModern(encoded string, passphrase []byte) ([]byte, error) {
+	const prefix = "WAGO1"
+	if len(encoded) < len(prefix) || encoded[:len(prefix)] != prefix {
+		return nil, errors.New("crypto: not a WAGO1 payload")
+	}
+	raw, err := base64.StdEncoding.DecodeString(encoded[len(prefix):])
+	if err != nil {
+		return nil, fmt.Errorf("crypto: base64 decode: %w", err)
+	}
+	if len(raw) < 16+12+16 {
+		return nil, errors.New("crypto: payload too short")
+	}
+	salt, nonce, ct := raw[:16], raw[16:28], raw[28:]
+
+	key := pbkdf2.Key(passphrase, salt, 100_000, 32, sha256.New)
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, err
+	}
+	pt, err := gcm.Open(nil, nonce, ct, nil)
+	if err != nil {
+		return nil, fmt.Errorf("crypto: decrypt failed: %w", err)
+	}
+	return pt, nil
+}
+
+// DerivePBKDF2SHA1 reproduces the C# Rfc2898DeriveBytes(password, salt,
+// 2000) used by the legacy WinAuth Encrypt/Decrypt sequence. The output
+// length matches PBKDF2_KEYSIZE / 8 from the original (32 bytes).
+func DerivePBKDF2SHA1(password, salt []byte) []byte {
+	return pbkdf2.Key(password, salt, legacyIterations, legacyKeySize, sha1.New)
+}