Add WireGuard TUI implementation

- Add Go TUI with bubbletea for WireGuard management
- Implement client CRUD operations with QR code generation
- Add configuration and validation modules
- Install/update scripts for client setup
- Update Makefile to build binaries to bin/ directory
- Add .gitignore for Go projects

internal/tui/model.go

@@ -0,0 +1,89 @@
+package screens
+
+import (
+	tea "github.com/charmbracelet/bubbletea"
+	"github.com/charmbracelet/lipgloss"
+)
+
+// Screen represents a UI screen (list, add, detail, etc.)
+type Screen interface {
+	Init() tea.Cmd
+	Update(tea.Msg) (Screen, tea.Cmd)
+	View() string
+}
+
+// Model is shared state across all screens
+type Model struct {
+	err           error
+	isQuitting    bool
+	ready         bool
+	statusMessage string
+	screen        Screen
+}
+
+// View renders the model (implements Screen interface)
+func (m *Model) View() string {
+	if m.err != nil {
+		return "\n" + lipgloss.NewStyle().
+			Foreground(lipgloss.Color("196")).
+			Render(m.err.Error())
+	}
+
+	if m.isQuitting {
+		return "\nGoodbye!\n"
+	}
+
+	if m.screen != nil {
+		return m.screen.View()
+	}
+
+	return "Initializing..."
+}
+
+// Init initializes the model
+func (m *Model) Init() tea.Cmd {
+	m.ready = true
+	return nil
+}
+
+// Update handles incoming messages (implements Screen interface)
+func (m *Model) Update(msg tea.Msg) (Screen, tea.Cmd) {
+	// If we have an error, let it persist for display
+	if m.err != nil {
+		switch msg := msg.(type) {
+		case tea.KeyMsg:
+			if msg.String() == "q" || msg.String() == "ctrl+c" {
+				m.isQuitting = true
+				return m, tea.Quit
+			}
+		}
+		return m, nil
+	}
+
+	// No error - handle normally
+	switch msg := msg.(type) {
+	case tea.KeyMsg:
+		switch msg.String() {
+		case "q", "ctrl+c":
+			m.isQuitting = true
+			return m, tea.Quit
+		}
+	}
+
+	return m, nil
+}
+
+// SetScreen changes the current screen
+func (m *Model) SetScreen(screen Screen) {
+	m.screen = screen
+}
+
+// SetError sets an error message
+func (m *Model) SetError(err error) {
+	m.err = err
+}
+
+// ClearError clears the error message
+func (m *Model) ClearError() {
+	m.err = nil
+}