feat(form): expose global keybinds at form level

[Kapparina]

Description

This pull request refactors the keymap instantiation process for the Form component:

• Introduces a defaultKeyMap to prevent redundant keymap creation.
• Updates Form to reuse the defaultKeyMap for efficiency.
• Adjusts KeyBinds, exposing what is currently the only "global" keybinding (the Quit binding) at the Form level.
• Does not change anything about how keybindings are displayed via standard (read: "bubbletea-less") usage; exposing the Quit binding to the ShortHelp() method is only done where a Form's Quit binding or help text differs from the default and one wishes to do so (see the attached example).

The primary use-case for this update is to cater for scenarios where the Quit binding differs from the default and must therefore be exposed to the user (a common example of when one might do this is when using a huh.Form in a bubbletea.Model as in the huh/bubbletea example).

Prerequisites

This PR relies upon charmbracelet/bubbles#773

Working Example

The following sample demonstrates this change, displaying both the Form's native help (Group/Field level) and that which is exposed at the Form level:

package main

import (
	"github.com/charmbracelet/bubbles/v2/key"
	tea "github.com/charmbracelet/bubbletea/v2"
	"github.com/charmbracelet/huh/v2"
	"github.com/charmbracelet/lipgloss/v2"
	"github.com/charmbracelet/lipgloss/v2/compat"
)

var (
	red    = compat.AdaptiveColor{Light: lipgloss.Color("#FE5F86"), Dark: lipgloss.Color("#FE5F86")}
	indigo = compat.AdaptiveColor{Light: lipgloss.Color("#5A56E0"), Dark: lipgloss.Color("#7571F9")}
	green  = compat.AdaptiveColor{Light: lipgloss.Color("#02BA84"), Dark: lipgloss.Color("#02BF87")}
)

type Styles struct {
	Base,
	HeaderText,
	Status,
	StatusHeader,
	Highlight,
	ErrorHeaderText,
	Help lipgloss.Style
}

func NewStyles() *Styles {
	s := Styles{}
	s.Base = lipgloss.NewStyle().
		Padding(1, 4, 0, 1)
	s.HeaderText = lipgloss.NewStyle().
		Foreground(indigo).
		Bold(true).
		Padding(0, 1, 0, 2)
	s.Status = lipgloss.NewStyle().
		Border(lipgloss.RoundedBorder()).
		BorderForeground(indigo).
		PaddingLeft(1).
		MarginTop(1)
	s.StatusHeader = lipgloss.NewStyle().
		Foreground(green).
		Bold(true)
	s.Highlight = lipgloss.NewStyle().
		Foreground(lipgloss.Color("212"))
	s.ErrorHeaderText = s.HeaderText.
		Foreground(red)
	s.Help = lipgloss.NewStyle().
		Foreground(lipgloss.Color("240"))
	return &s
}

func NewModel(form *huh.Form) tea.Model {
	var m TuiModel
	m.styles = NewStyles()
	m.form = form
	return m
}

type TuiModel struct {
	styles *Styles
	form   *huh.Form
}

func (t TuiModel) Init() tea.Cmd {
	k := huh.NewDefaultKeyMap()
	t.form = t.form.WithKeyMap(
		&huh.KeyMap{
			Quit: key.NewBinding(
				key.WithKeys("ctrl+c", "esc"),
				key.WithHelp("ctrl+c | esc", "Quit the program"),
			),
			Confirm:     k.Confirm,
			FilePicker:  k.FilePicker,
			Input:       k.Input,
			MultiSelect: k.MultiSelect,
			Note:        k.Note,
			Select:      k.Select,
			Text:        k.Text,
		},
	).WithWidth(100)
	return t.form.Init()
}

func (t TuiModel) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
	switch msg := msg.(type) {
	case tea.KeyMsg:
		switch msg.String() {
		case "ctrl+c", "esc":
			return t, tea.Quit
		}
	}
	var cmds []tea.Cmd
	form, cmd := t.form.Update(msg)
	if f, ok := form.(*huh.Form); ok {
		t.form = f
		cmds = append(cmds, cmd)
	}
	if t.form.State == huh.StateCompleted {
		cmds = append(cmds, tea.Quit)
	}
	return t, tea.Batch(cmds...)
}

func (t TuiModel) View() string {
	s := t.styles
	form := lipgloss.NewStyle().Render(t.form.View())
	body := lipgloss.JoinHorizontal(lipgloss.Top, form)
	footer := t.form.Help().ShortHelpView(t.form.KeyBinds())
	return s.Base.Render(body + "\n\n" + footer)
}

func main() {
	form := huh.NewForm(
		huh.NewGroup(
			huh.NewSelect[string]().
				Title("Select something").
				Options(
					huh.NewOptions[string]("one", "two")...,
				),
		),
	).WithShowHelp(true)

	model := NewModel(form)
	_, err := tea.NewProgram(model).Run()
	if err != nil {
		panic(err)
	}
}

Below is what the above sample looks like at runtime (note again that both help texts are shown for the sake of contrast):