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.frag

@@ -0,0 +1,24 @@
+#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;
+
+vec3 sRGBtoRGB(vec3 rgb) {
+	bvec3 cutoff = greaterThanEqual(rgb, vec3(0.04045));
+	vec3 below = rgb/vec3(12.92);
+	vec3 above = pow((rgb + vec3(0.055))/vec3(1.055), vec3(2.4));
+	return mix(below, above, cutoff);
+}
+
+void main() {
+	vec4 texel = texture(tex, vUV);
+	texel.rgb = sRGBtoRGB(texel.rgb);
+	fragColor = texel;
+}