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/shader/gio/copy.vert

@@ -0,0 +1,26 @@
+#version 310 es
+
+// SPDX-License-Identifier: Unlicense OR MIT
+
+#extension GL_GOOGLE_include_directive : enable
+
+precision highp float;
+
+#include "common.h"
+
+layout(push_constant) uniform Block {
+	vec2 scale;
+	vec2 pos;
+	vec2 uvScale;
+} _block;
+
+layout(location = 0) in vec2 pos;
+layout(location = 1) in vec2 uv;
+
+layout(location = 0) out vec2 vUV;
+
+void main() {
+	vUV = vec2(uv*_block.uvScale);
+	vec2 p = vec2(pos*_block.scale + _block.pos);
+	gl_Position = vec4(transform3x2(windowTransform, vec3(p, 0)), 1);
+}