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/material.frag

@@ -0,0 +1,32 @@
+#version 310 es
+
+// SPDX-License-Identifier: Unlicense OR MIT
+
+precision mediump float;
+
+layout(binding = 0) uniform sampler2D tex;
+
+layout(location = 0) in highp vec2 vUV;
+
+layout(location = 0) out vec4 fragColor;
+
+layout(push_constant) uniform Color {
+	// If emulateSRGB is set (!= 0), the input texels are sRGB encoded. We save the
+	// conversion step below, at the cost of texture filtering in sRGB space.
+	layout(offset=16) float emulateSRGB;
+} _color;
+
+vec3 RGBtosRGB(vec3 rgb) {
+	bvec3 cutoff = greaterThanEqual(rgb, vec3(0.0031308));
+	vec3 below = vec3(12.92)*rgb;
+	vec3 above = vec3(1.055)*pow(rgb, vec3(0.41666)) - vec3(0.055);
+	return mix(below, above, cutoff);
+}
+
+void main() {
+	vec4 texel = texture(tex, vUV);
+	if (_color.emulateSRGB == 0.0) {
+		texel.rgb = RGBtosRGB(texel.rgb);
+	}
+	fragColor = texel;
+}