chore(v2): vendor dependencies for offline/China builds

go mod vendor pins onnxruntime_go v1.12.1, Gio and the rest into v2/vendor
so go run/build work without hitting proxy.golang.org (blocked/slow in
China). Verified: CGO_ENABLED=1 go build -mod=vendor ./internal/spike and
GOOS=windows go build -mod=vendor ./internal/ui both pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

v2/vendor/gioui.org/widget/material/checkbox.go

@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package material
+
+import (
+	"gioui.org/io/semantic"
+	"gioui.org/layout"
+	"gioui.org/widget"
+)
+
+type CheckBoxStyle struct {
+	checkable
+	CheckBox *widget.Bool
+}
+
+func CheckBox(th *Theme, checkBox *widget.Bool, label string) CheckBoxStyle {
+	c := CheckBoxStyle{
+		CheckBox: checkBox,
+		checkable: checkable{
+			Label:              label,
+			Color:              th.Palette.Fg,
+			IconColor:          th.Palette.ContrastBg,
+			TextSize:           th.TextSize * 14.0 / 16.0,
+			Size:               26,
+			shaper:             th.Shaper,
+			checkedStateIcon:   th.Icon.CheckBoxChecked,
+			uncheckedStateIcon: th.Icon.CheckBoxUnchecked,
+		},
+	}
+	c.checkable.Font.Typeface = th.Face
+	return c
+}
+
+// Layout updates the checkBox and displays it.
+func (c CheckBoxStyle) Layout(gtx layout.Context) layout.Dimensions {
+	return c.CheckBox.Layout(gtx, func(gtx layout.Context) layout.Dimensions {
+		semantic.CheckBox.Add(gtx.Ops)
+		return c.layout(gtx, c.CheckBox.Value, c.CheckBox.Hovered() || gtx.Focused(c.CheckBox))
+	})
+}