Build UI & playground

As a way to play around with `little-owl`, we can build a small playground on [glitch](https://glitch.com) and offer a textarea to type in SQL. We should pick an interesting AWS public dataset and setup the Athena tables for it, and maybe offer a few example SQL queries. If the playground is hosted on glitch, users can then fork it and add their own AWS keys.

No file, test, or entry point is named. Start by reviewing little-owl's existing CLI and AWS Athena integration, then define the Glitch playground, public dataset, Athena tables, and example queries; done means users can enter SQL, run the examples, and fork the playground with their own AWS keys.

Written by the indexing model from the issue text.