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/input/doc.go

@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+/*
+Package input implements input routing and tracking of interface
+state for a window.
+
+The [Source] is the interface between the window and the widgets
+of a user interface and is exposed by [gioui.org/app.FrameEvent]
+received from windows.
+
+The [Router] is used by [gioui.org/app.Window] to track window state and route
+events from the platform to event handlers. It is otherwise only
+useful for using Gio with external window implementations.
+*/
+package input