Best approach to creating flat file scrum board web app?

I am looking for best approach on creating scrum board using flat files system only. I have been game developer for some time and I want to learn on creating flat file web apps. For this I want to create scrum board, like Scrum Board - I am good in html5 and Python - but since I have never created web app before, I wonder if html5 alone would be good approach and secure enough?

As of requirements - this system needs to be flat file (no databases at all) and needs to be secure and flexible while being easy to update globally.

How do I approach that? Thank you!