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.go

@@ -0,0 +1,132 @@
+package ui
+
+import (
+	"image/color"
+
+	"gioui.org/layout"
+	"gioui.org/unit"
+	"gioui.org/widget"
+	"gioui.org/widget/material"
+
+	"git.wxccs.org/iceking2nd/winauth-go/internal/authenticator"
+)
+
+// Dialog is the common contract implemented by every modal dialog.
+// onDone is invoked with the newly built authenticator + display name on
+// successful submission, or with (nil, "") on cancel.
+type Dialog interface {
+	Layout(gtx layout.Context, th *material.Theme,
+		onDone func(authenticator.Authenticator, string)) layout.Dimensions
+}
+
+// modalCard renders the standard backdrop + centered card with the given
+// title, body widget and an OK + Cancel button row. okLabel allows callers
+// to override the primary button label (e.g. "Enroll" for Battle.Net).
+//
+// The function does not handle the click events itself; callers should
+// query okBtn.Clicked / cancelBtn.Clicked before laying out so they can
+// short-circuit the frame.
+func modalCard(
+	gtx layout.Context,
+	th *material.Theme,
+	title string,
+	okLabel string,
+	cancelLabel string,
+	okBtn *widget.Clickable,
+	cancelBtn *widget.Clickable,
+	body layout.Widget,
+) layout.Dimensions {
+	fillBackground(gtx, color.NRGBA{R: 0, G: 0, B: 0, A: 0x60})
+
+	return layout.Center.Layout(gtx, func(gtx layout.Context) layout.Dimensions {
+		gtx.Constraints.Max.X = gtx.Dp(420)
+		return widget.Border{
+			Color:        color.NRGBA{R: 0x55, G: 0x55, B: 0x55, A: 0xff},
+			CornerRadius: unit.Dp(4),
+			Width:        unit.Dp(1),
+		}.Layout(gtx, func(gtx layout.Context) layout.Dimensions {
+			fillBackground(gtx, color.NRGBA{R: 0xff, G: 0xff, B: 0xff, A: 0xff})
+			return layout.UniformInset(unit.Dp(16)).Layout(gtx, func(gtx layout.Context) layout.Dimensions {
+				return layout.Flex{Axis: layout.Vertical}.Layout(gtx,
+					layout.Rigid(material.H6(th, title).Layout),
+					layout.Rigid(layout.Spacer{Height: unit.Dp(12)}.Layout),
+					layout.Rigid(body),
+					layout.Rigid(layout.Spacer{Height: unit.Dp(12)}.Layout),
+					layout.Rigid(func(gtx layout.Context) layout.Dimensions {
+						return layout.Flex{Axis: layout.Horizontal, Spacing: layout.SpaceStart}.Layout(gtx,
+							layout.Rigid(material.Button(th, cancelBtn, cancelLabel).Layout),
+							layout.Rigid(func(gtx layout.Context) layout.Dimensions {
+								return layout.Inset{Left: unit.Dp(8)}.Layout(gtx,
+									material.Button(th, okBtn, okLabel).Layout)
+							}),
+						)
+					}),
+				)
+			})
+		})
+	})
+}
+
+// modalCardCancel is a variant of modalCard with only a Cancel button.
+// Useful for dialogs whose primary actions live inside the body itself
+// (e.g. the QR scan dialog with separate "from file" / "from clipboard"
+// buttons).
+func modalCardCancel(
+	gtx layout.Context,
+	th *material.Theme,
+	title string,
+	cancelLabel string,
+	cancelBtn *widget.Clickable,
+	body layout.Widget,
+) layout.Dimensions {
+	fillBackground(gtx, color.NRGBA{R: 0, G: 0, B: 0, A: 0x60})
+
+	return layout.Center.Layout(gtx, func(gtx layout.Context) layout.Dimensions {
+		gtx.Constraints.Max.X = gtx.Dp(420)
+		return widget.Border{
+			Color:        color.NRGBA{R: 0x55, G: 0x55, B: 0x55, A: 0xff},
+			CornerRadius: unit.Dp(4),
+			Width:        unit.Dp(1),
+		}.Layout(gtx, func(gtx layout.Context) layout.Dimensions {
+			fillBackground(gtx, color.NRGBA{R: 0xff, G: 0xff, B: 0xff, A: 0xff})
+			return layout.UniformInset(unit.Dp(16)).Layout(gtx, func(gtx layout.Context) layout.Dimensions {
+				return layout.Flex{Axis: layout.Vertical}.Layout(gtx,
+					layout.Rigid(material.H6(th, title).Layout),
+					layout.Rigid(layout.Spacer{Height: unit.Dp(12)}.Layout),
+					layout.Rigid(body),
+					layout.Rigid(layout.Spacer{Height: unit.Dp(12)}.Layout),
+					layout.Rigid(func(gtx layout.Context) layout.Dimensions {
+						return layout.Flex{Axis: layout.Horizontal, Spacing: layout.SpaceStart}.Layout(gtx,
+							layout.Rigid(material.Button(th, cancelBtn, cancelLabel).Layout),
+						)
+					}),
+				)
+			})
+		})
+	})
+}
+
+// errorLabel returns a layout widget that renders msg in red, or nothing
+// when msg is empty. Used by dialogs to display validation errors.
+func errorLabel(th *material.Theme, msg string) layout.Widget {
+	return func(gtx layout.Context) layout.Dimensions {
+		if msg == "" {
+			return layout.Dimensions{}
+		}
+		lbl := material.Body2(th, msg)
+		lbl.Color = color.NRGBA{R: 0xc0, A: 0xff}
+		return layout.Inset{Top: unit.Dp(8)}.Layout(gtx, lbl.Layout)
+	}
+}
+
+// labeledEditor lays out a small body label above the editor. hint is the
+// editor placeholder text.
+func labeledEditor(th *material.Theme, label string, ed *widget.Editor, hint string) layout.Widget {
+	return func(gtx layout.Context) layout.Dimensions {
+		return layout.Flex{Axis: layout.Vertical}.Layout(gtx,
+			layout.Rigid(material.Body2(th, label).Layout),
+			layout.Rigid(material.Editor(th, ed, hint).Layout),
+			layout.Rigid(layout.Spacer{Height: unit.Dp(8)}.Layout),
+		)
+	}
+}