feat(label): edit a label in a form without flags

label edit without flags on a terminal now opens a form with the label's
name, color, description and flags, like milestone edit and issue edit,
instead of failing; without a terminal it reports the shared "nothing to
edit" error. The help of issue and milestone close and reopen names its
commands without generating the text from the verb.

Signed-off-by: bircni <bircni@icloud.com>

internal/terminal/label_form_test.go

@@ -0,0 +1,28 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package terminal
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestLabelFormStartsFromCurrentValues(t *testing.T) {
+	p, _ := testPrompter(strings.NewReader("\r\r\r\r\r"))
+	current := LabelFormValues{Name: "bug", Color: "#EE0701", Description: "Broken", Exclusive: true}
+	values, err := p.EditLabel(context.Background(), `Editing label "bug" in alice/x`, current)
+	require.NoError(t, err)
+	require.Equal(t, LabelFormValues{Name: "bug", Color: "EE0701", Description: "Broken", Exclusive: true}, values)
+}
+
+func TestLabelFormMarksNameRequired(t *testing.T) {
+	p, rendered := accessiblePrompter(t, "bug\nee0701\n\nn\nn\n")
+	values, err := p.EditLabel(context.Background(), "", LabelFormValues{})
+	require.NoError(t, err)
+	require.Contains(t, rendered.String(), "Label name (required):")
+	require.Equal(t, "bug", values.Name)
+}