feat: add /settings command and document /history for UI-command parity

- Add /settings command handler with inline settings keyboard
- Add /history to README commands table
- Update /help command list
- Remove unused Leagu.go old reference

internal/handler/handler.go

@@ -148,6 +148,8 @@ func (h *Handler) routeCommand(ctx context.Context, msg *models.Message, user *d
 	switch cmd {
 	case "/start":
 		h.handleStart(ctx, msg, user)
+	case "/settings":
+		h.handleSettings(ctx, msg, user)
 	case "/help":
 		h.handleHelp(ctx, msg)
 	case "/clockin":