I just signed up, and it seems like a cool app.
Technical issue: Email verification should not block the signup flow. I signed up, but the verification email went to the spam folder. Not a huge issue except I couldn't login until I went digging through the spam folder. You shouldn't really need to have users verify their emails for this app.
Product suggestion: Allow users to write their own prompt in addition to the three sample ones. Also consider letting people see a preview of the book before they finish the first conversation.
Marketing/positioning tip: I don't have any interest in writing about myself, but I would be interested in getting down some family stories from elderly relatives. Consider marketing this to people who want to get family stories (or life stories of elderly relatives) written down. Assume that the users will be sitting with their relatives and jotting down their responses.
Thanks for sharing your story. I think it's pretty impressive that this is your first web app and you were able to learn how to make it and create it in only a year. If you're willing to keep trying out new use cases, you may find some people who are interested. Good luck on this side project or your next one!
How many cold emails do you think you need to send to get one customer?