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.go

@@ -0,0 +1,49 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package terminal
+
+import (
+	"context"
+	"errors"
+	"regexp"
+	"strings"
+
+	"charm.land/huh/v2"
+)
+
+// LabelFormValues holds interactively edited label fields.
+type LabelFormValues struct {
+	Name, Color, Description string
+	Exclusive, Archived      bool
+}
+
+// LabelForm collects interactive label input.
+type LabelForm interface {
+	// EditLabel asks for the fields of a label, starting from current, under heading, such as
+	// `Editing label "bug" in alice/x`.
+	EditLabel(ctx context.Context, heading string, current LabelFormValues) (LabelFormValues, error)
+}
+
+var hexColor = regexp.MustCompile(`^#?[0-9a-fA-F]{6}$`)
+
+// EditLabel runs the interactive label form on stderr.
+func (p *FormPrompter) EditLabel(ctx context.Context, heading string, current LabelFormValues) (LabelFormValues, error) {
+	values := current
+	if err := p.runForm(ctx, huh.NewForm(huh.NewGroup(
+		huh.NewInput().Title("Label name (required):").Value(&values.Name).Validate(huh.ValidateNotEmpty()),
+		huh.NewInput().Title("Color (hex, e.g. d73a4a):").Value(&values.Color).Validate(func(s string) error {
+			if !hexColor.MatchString(strings.TrimSpace(s)) {
+				return errors.New("use six hexadecimal digits")
+			}
+			return nil
+		}),
+		huh.NewInput().Title("Description (optional):").Value(&values.Description),
+		huh.NewConfirm().Title("Exclusive (one label of its scope per issue):").Value(&values.Exclusive),
+		huh.NewConfirm().Title("Archived:").Value(&values.Archived),
+	).Title(heading))); err != nil {
+		return LabelFormValues{}, err
+	}
+	values.Name, values.Color = strings.TrimSpace(values.Name), strings.TrimPrefix(strings.TrimSpace(values.Color), "#")
+	return values, nil
+}