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/op/clip/doc.go

@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+/*
+Package clip provides operations for defining areas that applies to operations
+such as paints and pointer handlers.
+
+The current clip is initially the infinite set. Pushing an Op sets the clip
+to the intersection of the current clip and pushed clip area. Popping the
+area restores the clip to its state before pushing.
+
+General clipping areas are constructed with Path. Common cases such as
+rectangular clip areas also exist as convenient constructors.
+*/
+package clip