The correct statement is Zoé est polie et forte.
Zoé est poli et fort is grammatically incorrect. In French, adjectives must agree with the noun they modify in gender and number. In this case, the adjective fort should be feminine to agree with the feminine noun Zoé.
Zoé est polie et forte. is grammatically correct, but it is not idiomatic. In French, it is more common to use the plural form of adjectives when describing a person's qualities.
Zoé est polie et fort. is grammatically correct and idiomatic. It means "Zoé is polite and strong."
Therefore, the correct statement is Zoé est polie et forte.