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/runmain.go

@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+//go:build android || (darwin && ios)
+
+package app
+
+// Android only supports non-Java programs as c-shared libraries.
+// Unfortunately, Go does not run a program's main function in
+// library mode. To make Gio programs simpler and uniform, we'll
+// link to the main function here and call it from Java.
+
+import (
+	"sync"
+	_ "unsafe" // for go:linkname
+)
+
+//go:linkname mainMain main.main
+func mainMain()
+
+var runMainOnce sync.Once
+
+func runMain() {
+	runMainOnce.Do(func() {
+		// Indirect call, since the linker does not know the address of main when
+		// laying down this package.
+		fn := mainMain
+		go fn()
+	})
+}