feat(ui): 主题切换 + 语言持久化 + About 对话框

- 新增 light/dark 主题调色板与 Windows 注册表系统主题探测
- 偏好设置对话框：主题三选一 + 语言下拉(en/zh-CN/de)，即时生效
- 持久化 Language/Theme/AutoLockMinutes/MinimizeToTray 至 YAML 顶层
- 启动时按 config 中保存的语言初始化 i18n
- About 对话框展示 version/runtime/项目地址/许可证
- 全部硬编码颜色迁移到 themePalette，为深色模式做准备

internal/ui/dialog_about.go

@@ -0,0 +1,55 @@
+package ui
+
+import (
+	"runtime"
+
+	"gioui.org/layout"
+	"gioui.org/unit"
+	"gioui.org/widget"
+	"gioui.org/widget/material"
+
+	"git.wxccs.org/iceking2nd/winauth-go/internal/i18n"
+	"git.wxccs.org/iceking2nd/winauth-go/internal/version"
+)
+
+// aboutDialog is a read-only popup describing the build, runtime and a
+// short credits / project link blurb. Click "Close" to dismiss.
+type aboutDialog struct {
+	closeBt widget.Clickable
+}
+
+func newAboutDialog() *aboutDialog { return &aboutDialog{} }
+
+// Layout follows the simpler "single button" contract: onDone is called
+// with no arguments when the user dismisses the dialog.
+func (d *aboutDialog) Layout(
+	gtx layout.Context, th *material.Theme,
+	onDone func(),
+) layout.Dimensions {
+	if d.closeBt.Clicked(gtx) {
+		onDone()
+		return layout.Dimensions{Size: gtx.Constraints.Max}
+	}
+
+	body := func(gtx layout.Context) layout.Dimensions {
+		line := func(text string) layout.FlexChild {
+			return layout.Rigid(func(gtx layout.Context) layout.Dimensions {
+				return layout.Inset{Top: unit.Dp(2), Bottom: unit.Dp(2)}.Layout(gtx,
+					material.Body2(th, text).Layout)
+			})
+		}
+		return layout.Flex{Axis: layout.Vertical}.Layout(gtx,
+			line(i18n.T("about_app_name")),
+			line(i18n.T("about_version_label")+": "+version.String()),
+			line(i18n.T("about_runtime_label")+": "+runtime.Version()+" ("+runtime.GOOS+"/"+runtime.GOARCH+")"),
+			layout.Rigid(layout.Spacer{Height: unit.Dp(8)}.Layout),
+			line(i18n.T("about_project_label")+": "+i18n.T("about_project_url")),
+			line(i18n.T("about_license_label")+": "+i18n.T("about_license_value")),
+			layout.Rigid(layout.Spacer{Height: unit.Dp(8)}.Layout),
+			line(i18n.T("about_credits")),
+		)
+	}
+
+	return modalCardCancel(gtx, th, i18n.T("dialog_about_title"),
+		i18n.T("btn_close"), &d.closeBt, body)
+}