fix(cli): route frame UI to stderr

Co-Authored-By: Virgil <virgil@lethean.io>

pkg/cli/frame.go

@@ -61,7 +61,7 @@ func NewFrame(variant string) *Frame {
 		variant: variant,
 		layout:  Layout(variant),
 		models:  make(map[Region]Model),
-		out:     os.Stdout,
+		out:     os.Stderr,
 		done:    make(chan struct{}),
 		focused: RegionContent,
 		keyMap:  DefaultKeyMap(),

pkg/cli/frame_test.go

@@ -2,6 +2,7 @@ package cli
 
 import (
 	"bytes"
+	"os"
 	"strings"
 	"testing"
 	"time"
@@ -136,6 +137,11 @@ func TestFrame_Good(t *testing.T) {
 		assert.Less(t, elapsed, 200*time.Millisecond)
 		assert.Contains(t, buf.String(), "timed")
 	})
+
+	t.Run("default output goes to stderr", func(t *testing.T) {
+		f := NewFrame("C")
+		assert.Same(t, os.Stderr, f.out)
+	})
 }
 
 func TestFrame_Bad(t *testing.T) {