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/ui/dialog_password.go

@@ -0,0 +1,69 @@
+package ui
+
+import (
+	"gioui.org/layout"
+	"gioui.org/widget"
+	"gioui.org/widget/material"
+
+	"git.wxccs.org/iceking2nd/winauth-go/internal/i18n"
+)
+
+// passwordDialog asks the user for the password to decrypt an existing
+// config. The dialog is shown at startup when the config file is found
+// to be encrypted; on submit it calls onDone with the entered passphrase.
+// Cancel returns an empty passphrase and signals abort.
+type passwordDialog struct {
+	prompt   string // optional explanatory line above the field
+	errorMsg string
+
+	pwEd      widget.Editor
+	okBtn     widget.Clickable
+	cancelBtn widget.Clickable
+}
+
+func newPasswordDialog(prompt string) *passwordDialog {
+	d := &passwordDialog{prompt: prompt}
+	d.pwEd.SingleLine = true
+	d.pwEd.Mask = '*'
+	return d
+}
+
+// SetError lets the caller surface a "wrong password" message after a
+// failed Load attempt, so the same dialog can be reused for a retry loop.
+func (d *passwordDialog) SetError(msg string) { d.errorMsg = msg }
+
+// Layout takes onDone(password, ok). ok=true on submit; ok=false on cancel.
+// On ok the password slice is freshly allocated (the editor's underlying
+// buffer is not retained).
+func (d *passwordDialog) Layout(
+	gtx layout.Context, th *material.Theme,
+	onDone func(password []byte, ok bool),
+) layout.Dimensions {
+	if d.okBtn.Clicked(gtx) {
+		pw := []byte(d.pwEd.Text())
+		onDone(pw, true)
+		return layout.Dimensions{Size: gtx.Constraints.Max}
+	}
+	if d.cancelBtn.Clicked(gtx) {
+		onDone(nil, false)
+		return layout.Dimensions{Size: gtx.Constraints.Max}
+	}
+
+	body := func(gtx layout.Context) layout.Dimensions {
+		children := []layout.FlexChild{}
+		if d.prompt != "" {
+			children = append(children,
+				layout.Rigid(material.Body2(th, d.prompt).Layout),
+				layout.Rigid(layout.Spacer{Height: 8}.Layout),
+			)
+		}
+		children = append(children,
+			layout.Rigid(labeledEditor(th, i18n.T("label_password"), &d.pwEd, "")),
+			layout.Rigid(errorLabel(th, d.errorMsg)),
+		)
+		return layout.Flex{Axis: layout.Vertical}.Layout(gtx, children...)
+	}
+	return modalCard(gtx, th, i18n.T("dialog_password_title"),
+		i18n.T("btn_ok"), i18n.T("btn_cancel"),
+		&d.okBtn, &d.cancelBtn, body)
+}