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/border.go

@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package widget
+
+import (
+	"image"
+	"image/color"
+
+	"gioui.org/layout"
+	"gioui.org/op/clip"
+	"gioui.org/op/paint"
+	"gioui.org/unit"
+)
+
+// Border lays out a widget and draws a border inside it.
+type Border struct {
+	Color        color.NRGBA
+	CornerRadius unit.Dp
+	Width        unit.Dp
+}
+
+func (b Border) Layout(gtx layout.Context, w layout.Widget) layout.Dimensions {
+	dims := w(gtx)
+	sz := dims.Size
+
+	rr := gtx.Dp(b.CornerRadius)
+	width := gtx.Dp(b.Width)
+	whalf := (width + 1) / 2
+	sz.X -= whalf * 2
+	sz.Y -= whalf * 2
+
+	r := image.Rectangle{Max: sz}
+	r = r.Add(image.Point{X: whalf, Y: whalf})
+
+	paint.FillShape(gtx.Ops,
+		b.Color,
+		clip.Stroke{
+			Path:  clip.UniformRRect(r, rr).Path(gtx.Ops),
+			Width: float32(width),
+		}.Op(),
+	)
+
+	return dims
+}