what is too hot or too cold varies considerably by type of seed. Parsley seed needs to be soaked overnight first and germinates best at temps between 80-85. But note for many of these seeds, germination temperature is different from the temperature the seedlings like once they are growing. Parsley actually likes cool weather better and will grow better with temperatures around 50. It can handle temperatures down around 40 or even less once it is a sturdy little plant, well established and hardened off (gradually acclimatized to lower temperatures). Temperatures that plants can handle when hardened will kill them in a sudden drop.
Yes, I think your seeds were probably cooked. If you had your greenhouse in full sun, zipped up, it probably got well above 100 in there. It's called the "greenhouse effect" and it is what is doing our planet in. Very powerful.
Cilantro germinates best at temperatures from 55 to 70. The seeds need light to germinate, so do not cover them, just press them down lightly so they are in good contact with the potting mix. Cilantro is also a cool weather plant that fizzles as soon as it gets hot. It can stand temperatures down to freezing, once germinated and hardened.
You can look up for each seed the conditions it needs. I deal with having seeds that need heat and seeds that don't all in the same little greenhouse by having some on a heat mat and some not.
Here's a thread we had on seed starting basics: https://www.helpfulgardener.com/forum/vi ... 48&t=44183