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/zcover.vert.0.glsl100es

@@ -0,0 +1,51 @@
+#version 100
+
+struct m3x2
+{
+    vec3 r0;
+    vec3 r1;
+};
+
+struct Block
+{
+    vec4 transform;
+    vec4 uvCoverTransform;
+    vec4 uvTransformR1;
+    vec4 uvTransformR2;
+    float fbo;
+};
+
+uniform Block _block;
+
+attribute vec2 pos;
+varying vec2 vUV;
+attribute vec2 uv;
+varying vec2 vCoverUV;
+
+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()
+{
+    vec2 p = vec2((pos * _block.transform.xy) + _block.transform.zw);
+    if (_block.fbo != 0.0)
+    {
+        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);
+    }
+    else
+    {
+        m3x2 param_2 = m3x2(vec3(1.0, 0.0, 0.0), vec3(0.0, -1.0, 0.0));
+        vec3 param_3 = vec3(p, 0.0);
+        gl_Position = vec4(transform3x2(param_2, param_3), 1.0);
+    }
+    m3x2 param_4 = m3x2(_block.uvTransformR1.xyz, _block.uvTransformR2.xyz);
+    vec3 param_5 = vec3(uv, 1.0);
+    vUV = transform3x2(param_4, param_5).xy;
+    vec3 uv3 = vec3(uv, 1.0);
+    vCoverUV = ((uv3 * vec3(_block.uvCoverTransform.xy, 1.0)) + vec3(_block.uvCoverTransform.zw, 0.0)).xy;
+}
+