v0.8.0: add startup banner before entering alternate screen

Prints ';; Passepartout TUI starting...' before entering alternate screen,
so even if ANSI rendering fails, the user sees something.

org/channel-tui-main.org

@@ -880,6 +880,8 @@ Returns T on success, nil on failure. Does NOT wait or retry."
 (defvar *tty-in* nil "Stream from cat subprocess stdout (unused — direct stdin reads)")
 
 (defun tui-main ()
+  (format t "~&;; Passepartout TUI starting...~%")
+  (finish-output)
   (init-state)
   (load-history)
   (theme-load)