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/unit/unit.go

@@ -0,0 +1,78 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+/*
+Package unit implements device independent units.
+
+Device independent pixel, or dp, is the unit for sizes independent of
+the underlying display device.
+
+Scaled pixels, or sp, is the unit for text sizes. An sp is like dp with
+text scaling applied.
+
+Finally, pixels, or px, is the unit for display dependent pixels. Their
+size vary between platforms and displays.
+
+To maintain a constant visual size across platforms and displays, always
+use dps or sps to define user interfaces. Only use pixels for derived
+values.
+*/
+package unit
+
+import (
+	"math"
+)
+
+// Metric converts Values to device-dependent pixels, px. The zero
+// value represents a 1-to-1 scale from dp, sp to pixels.
+type Metric struct {
+	// PxPerDp is the device-dependent pixels per dp.
+	PxPerDp float32
+	// PxPerSp is the device-dependent pixels per sp.
+	PxPerSp float32
+}
+
+type (
+	// Dp represents device independent pixels. 1 dp will
+	// have the same apparent size across platforms and
+	// display resolutions.
+	Dp float32
+	// Sp is like UnitDp but for font sizes.
+	Sp float32
+)
+
+// Dp converts v to pixels, rounded to the nearest integer value.
+func (c Metric) Dp(v Dp) int {
+	return int(math.Round(float64(nonZero(c.PxPerDp)) * float64(v)))
+}
+
+// Sp converts v to pixels, rounded to the nearest integer value.
+func (c Metric) Sp(v Sp) int {
+	return int(math.Round(float64(nonZero(c.PxPerSp)) * float64(v)))
+}
+
+// DpToSp converts v dp to sp.
+func (c Metric) DpToSp(v Dp) Sp {
+	return Sp(float32(v) * nonZero(c.PxPerDp) / nonZero(c.PxPerSp))
+}
+
+// SpToDp converts v sp to dp.
+func (c Metric) SpToDp(v Sp) Dp {
+	return Dp(float32(v) * nonZero(c.PxPerSp) / nonZero(c.PxPerDp))
+}
+
+// PxToSp converts v px to sp.
+func (c Metric) PxToSp(v int) Sp {
+	return Sp(float32(v) / nonZero(c.PxPerSp))
+}
+
+// PxToDp converts v px to dp.
+func (c Metric) PxToDp(v int) Dp {
+	return Dp(float32(v) / nonZero(c.PxPerDp))
+}
+
+func nonZero(v float32) float32 {
+	if v == 0. {
+		return 1
+	}
+	return v
+}