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/internal/debug/debug.go

@@ -0,0 +1,57 @@
+// Package debug provides general debug feature management for Gio, including
+// the ability to toggle debug features using the GIODEBUG environment variable.
+package debug
+
+import (
+	"fmt"
+	"os"
+	"strings"
+	"sync"
+	"sync/atomic"
+)
+
+const (
+	debugVariable = "GIODEBUG"
+	textSubsystem = "text"
+	silentFeature = "silent"
+)
+
+// Text controls whether the text subsystem has debug logging enabled.
+var Text atomic.Bool
+
+var parseOnce sync.Once
+
+// Parse processes the current value of GIODEBUG. If it is unset, it does nothing.
+// Otherwise it process its value, printing usage info the stderr if the value is
+// not understood. Parse will be automatically invoked when the first application
+// window is created, allowing applications to manipulate GIODEBUG programmatically
+// before it is parsed.
+func Parse() {
+	parseOnce.Do(func() {
+		val, ok := os.LookupEnv(debugVariable)
+		if !ok {
+			return
+		}
+		print := false
+		silent := false
+		for part := range strings.SplitSeq(val, ",") {
+			switch part {
+			case textSubsystem:
+				Text.Store(true)
+			case silentFeature:
+				silent = true
+			default:
+				print = true
+			}
+		}
+		if print && !silent {
+			fmt.Fprintf(os.Stderr,
+				`Usage of %s:
+	A comma-delimited list of debug subsystems to enable. Currently recognized systems:
+
+	- %s: text debug info including system font resolution
+	- %s: silence this usage message even if GIODEBUG contains invalid content
+`, debugVariable, textSubsystem, silentFeature)
+		}
+	})
+}