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/intersect.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(location = 0) in vec2 pos;
+layout(location = 1) in vec2 uv;
+
+layout(push_constant) uniform Block {
+	vec4 uvTransform;
+	vec4 subUVTransform;
+} _block;
+
+layout(location = 0) out vec2 vUV;
+
+void main() {
+  vec3 p = transform3x2(fboTransform, vec3(pos, 1.0));
+  gl_Position = vec4(p, 1);
+  vUV = uv.xy*_block.subUVTransform.xy + _block.subUVTransform.zw;
+  vUV = vUV*_block.uvTransform.xy + _block.uvTransform.zw;
+}