Does divorce take effect if the wife says to the waiter, "Here is my heart," without intending it, knowing that the husband stipulated for divorce to occur—as a condition for talking to men—that it must be intentional?

As long as your husband did not condition your divorce on speaking to men unintentionally, your divorce did not occur by the statement you made to the waiter without intent. However, you must fear Allah, control your words, and not be complacent in speaking with non-mahram (definition) men in such a manner, for it is a great door to temptation and an entry point for those with weak souls to covet. Allah Almighty says: "O wives of the Prophet, you are not like any other women. If you fear Allah, then do not be soft in speech [to men], lest he in whose heart is disease should covet, but speak with appropriate speech" (Al-Ahzab: 32). This means you should not address non-mahram men with speech that is soft or gentle.