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/cover.vert

@@ -0,0 +1,37 @@
+#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 {
+	vec4 transform;
+	vec4 uvCoverTransform;
+	vec4 uvTransformR1;
+	vec4 uvTransformR2;
+	// fbo is set if blitting to a FBO, otherwise the window.
+	float fbo;
+} _block;
+
+layout(location = 0) in vec2 pos;
+
+layout(location = 0) out vec2 vCoverUV;
+
+layout(location = 1) in vec2 uv;
+layout(location = 1) out vec2 vUV;
+
+void main() {
+	vec2 p = vec2(pos*_block.transform.xy + _block.transform.zw);
+	if (_block.fbo != 0.0) {
+		gl_Position = vec4(transform3x2(fboTransform, vec3(p, 0)), 1);
+	} else {
+		gl_Position = vec4(transform3x2(windowTransform, vec3(p, 0)), 1);
+	}
+	vUV = transform3x2(m3x2(_block.uvTransformR1.xyz, _block.uvTransformR2.xyz), vec3(uv,1)).xy;
+	vec3 uv3 = vec3(uv, 1.0);
+	vCoverUV = (uv3*vec3(_block.uvCoverTransform.xy, 1.0)+vec3(_block.uvCoverTransform.zw, 0.0)).xy;
+}