Unless otherwise specified, you have no license to use any code you find on the Internet.

With short code snippets, you arguably don’t need a license. Only if it’s notable enough to get copyright protection do you need permission to use it, right? I can copy hello world examples from websites and do whatever I want with them, I think.

I don't necessarily disagree (I am not a lawyer), my point is that reading an AGPL license at the bottom of the page can only be a good thing; it can only give you the ability to do more things than you could if had no notice been there.

That depends on the jurisdiction.

Very little, though. See the map:

https://en.wikipedia.org/wiki/Berne_Convention