So since I expect other people will do the same thing, I'm going to say what I did (my account is apparently unusable, and theoretically it's my fault, but there doesn't appear to be any functioning way to recover from it):
1. When I saw that spam email (at like 4 in the morning, although I am unsure if that even mattered), I clicked the activation link without reading the email, and then closed the page it opened without reading that either. (I never read either; this would be the first I've ever run into which required doing so)
2. Today when I started the client, I still got the red screen. I did not know why, and thought that was strange because I had activated.
3. I clicked through that and clicked login and I got the red screen again. It did not ask for anything, it just errored. Very confusing.
4. I click 'use different account' and realize I don't have a username or password to enter, and it isn't asking for either one besides. It wants an "id" and "key."
5. I glance at the email and paste in the id and key I see there.
6. It doesn't work. I read further in the email and see "This activation key is a one-time key and is not the player key you need to play the game. You will get the player key when you activate your account (e.g. click on the link above)."
7. I realize my account is unusable.
8. I click forgot id or key. Nothing appears to happen.
9. I check my email. No new emails.
10. I check my spam folder. No new emails there either.
11. I say "welp" and start typing up this post.
Edit: To be clear, I'm not saying "help my account is unusable" (I could make another and just read the page this time*). I'm saying "perhaps you might want to re-think how you're doing this, because I bet this will happen a lot when you have a general audience trying to sign up this way."
* assuming it lets me, since I already used my email once (apparently I get a server error if I try, although perhaps that really is a server error - who knows)