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/font/gofont/gofont.go

@@ -0,0 +1,83 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+// Package gofont exports the Go fonts as a text.Collection.
+//
+// See https://blog.golang.org/go-fonts for a description of the
+// fonts, and the golang.org/x/image/font/gofont packages for the
+// font data.
+package gofont
+
+import (
+	"fmt"
+	"sync"
+
+	"golang.org/x/image/font/gofont/gobold"
+	"golang.org/x/image/font/gofont/gobolditalic"
+	"golang.org/x/image/font/gofont/goitalic"
+	"golang.org/x/image/font/gofont/gomedium"
+	"golang.org/x/image/font/gofont/gomediumitalic"
+	"golang.org/x/image/font/gofont/gomono"
+	"golang.org/x/image/font/gofont/gomonobold"
+	"golang.org/x/image/font/gofont/gomonobolditalic"
+	"golang.org/x/image/font/gofont/gomonoitalic"
+	"golang.org/x/image/font/gofont/goregular"
+	"golang.org/x/image/font/gofont/gosmallcaps"
+	"golang.org/x/image/font/gofont/gosmallcapsitalic"
+
+	"gioui.org/font"
+	"gioui.org/font/opentype"
+)
+
+var (
+	regOnce    sync.Once
+	reg        []font.FontFace
+	once       sync.Once
+	collection []font.FontFace
+)
+
+func loadRegular() {
+	regOnce.Do(func() {
+		faces, err := opentype.ParseCollection(goregular.TTF)
+		if err != nil {
+			panic(fmt.Errorf("failed to parse font: %v", err))
+		}
+		reg = faces
+		collection = append(collection, reg[0])
+	})
+}
+
+// Regular returns a collection of only the Go regular font face.
+func Regular() []font.FontFace {
+	loadRegular()
+	return reg
+}
+
+// Regular returns a collection of all available Go font faces.
+func Collection() []font.FontFace {
+	loadRegular()
+	once.Do(func() {
+		register(goitalic.TTF)
+		register(gobold.TTF)
+		register(gobolditalic.TTF)
+		register(gomedium.TTF)
+		register(gomediumitalic.TTF)
+		register(gomono.TTF)
+		register(gomonobold.TTF)
+		register(gomonobolditalic.TTF)
+		register(gomonoitalic.TTF)
+		register(gosmallcaps.TTF)
+		register(gosmallcapsitalic.TTF)
+		// Ensure that any outside appends will not reuse the backing store.
+		n := len(collection)
+		collection = collection[:n:n]
+	})
+	return collection
+}
+
+func register(ttf []byte) {
+	faces, err := opentype.ParseCollection(ttf)
+	if err != nil {
+		panic(fmt.Errorf("failed to parse font: %v", err))
+	}
+	collection = append(collection, faces[0])
+}