This subdivision of the verb 'to be' occurs in Spanish and Portuguese, and it serves basically to separate between permanent and transient states.' 'Estás lista' is basically asking if the person in question is ready at the time of asking. You can say that you "estás listo" but you cannot say that you "estás de Sudan". That would sound weird and in a sense, imply that you are 'of Sudan' today, but you may be 'of somewhere else' tomorrow. And likewise, you cannot say that you "es listo". That would imply that you are ready as sort of a personal trait. For permanent states, you use 'Ser', for transient states that have a time limitation on them you use "Estar". Hope that answers your question.

Estás can mean these, but most people do use estás listo/lista as "are you ready?"

It depends on how you use it

Depende del contexto. Tiene varios significados.

in spanish there are not "to be" verb, we have two verbs "ser" y "estar", "¿estás?" (with questions mark) can means "¿estás allí? (are you there?) or "¿estás lista?" (are your ready?).