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/io/clipboard/clipboard.go

@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package clipboard
+
+import (
+	"io"
+
+	"gioui.org/io/event"
+)
+
+// WriteCmd copies Text to the clipboard.
+type WriteCmd struct {
+	Type string
+	Data io.ReadCloser
+}
+
+// ReadCmd requests the text of the clipboard, delivered to
+// the handler through an [io/transfer.DataEvent].
+type ReadCmd struct {
+	Tag event.Tag
+}
+
+func (WriteCmd) ImplementsCommand() {}
+func (ReadCmd) ImplementsCommand()  {}