Avoid flicker when starting kittens such as the hints kitten

Fixes #4674

kittens/tui/operations.py

@@ -413,6 +413,11 @@ def restore_colors() -> str:
     return '\x1b[#Q'
 
 
+@cmd
+def overlay_ready() -> str:
+    return '\x1bP@kitty-overlay-ready|\x1b\\'
+
+
 @cmd
 def write_to_clipboard(data: Union[str, bytes], use_primary: bool = False) -> str:
     from base64 import standard_b64encode