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/zcopy.vert.0.glsl100es

@@ -0,0 +1,35 @@
+#version 100
+
+struct m3x2
+{
+    vec3 r0;
+    vec3 r1;
+};
+
+struct Block
+{
+    vec2 scale;
+    vec2 pos;
+    vec2 uvScale;
+};
+
+uniform Block _block;
+
+varying vec2 vUV;
+attribute vec2 uv;
+attribute vec2 pos;
+
+vec3 transform3x2(m3x2 t, vec3 v)
+{
+    return vec3(dot(t.r0, v), dot(t.r1, v), dot(vec3(0.0, 0.0, 1.0), v));
+}
+
+void main()
+{
+    vUV = vec2(uv * _block.uvScale);
+    vec2 p = vec2((pos * _block.scale) + _block.pos);
+    m3x2 param = m3x2(vec3(1.0, 0.0, 0.0), vec3(0.0, -1.0, 0.0));
+    vec3 param_1 = vec3(p, 0.0);
+    gl_Position = vec4(transform3x2(param, param_1), 1.0);
+}
+