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/app/os_darwin.m

@@ -0,0 +1,11 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+#import <Foundation/Foundation.h>
+
+#include "_cgo_export.h"
+
+void gio_runOnMain(uintptr_t h) {
+	dispatch_async(dispatch_get_main_queue(), ^{
+		gio_runFunc(h);
+	});
+}