Integrate tournament sync via challonge API

[starcraft66]

We should disallow manual edits to tournaments via the tournaments page and instead have either an incoming webhook and/or a polling GenServer task sync the tournaments from the service into our database.

https://api.challonge.com/v1

[starcraft66]

Challonge API is now v2.1: https://api.challonge.com/v2.1

https://challonge.apidog.io/getting-started-1726706m0

🔔 Please note that effective March 2026, our API requires a paid plan should you need more than 5,000* requests per month (* subject to change prior to official announcement). You can upgrade your app from the Developer Portal.