feat: add navigation and window size handlers with corresponding tests

internal/handlers/helpHandler.go

@@ -0,0 +1,38 @@
+package handlers
+
+import (
+	"slices"
+
+	"github.com/StevanFreeborn/term-tier/internal/state"
+	tea "github.com/charmbracelet/bubbletea"
+)
+
+type helpHandler struct {
+	keys        []string
+	description string
+}
+
+func NewHelpHandler() KeyMsgHandler {
+	return helpHandler{
+		keys:        []string{"?"},
+		description: "Toggle help menu",
+	}
+}
+
+func (h helpHandler) KeysHandled() []string {
+	return h.keys
+}
+
+func (h helpHandler) Description() string {
+	return h.description
+}
+
+func (h helpHandler) Match(s state.State, msg tea.KeyMsg) bool {
+	return s.Mode() == state.NavigationMode && slices.Contains(h.keys, msg.String()) ||
+		s.Mode() == state.HelpMode && slices.Contains(h.keys, msg.String())
+}
+
+func (h helpHandler) Handle(s state.State, msg tea.KeyMsg) tea.Cmd {
+	s.ToggleHelp()
+	return nil
+}