Update: the site’s back up and running.
The tech support at Media Temple said that we didn’t need to do anything to get our site back up. So we didn’t do anything, trusting they’d take care of it. Apparently, we did need to do something: we needed to bug them.
Frustrated that the site was still down, six hours after they said they’d take care of it, we got on the phone to ask them why it was still down, especially when their “system status” page said that all affected websites were “online” (as of several hours ago). They did something to escalate it in their system, and, bottom line: the site is back up.
Once again, let me apologize for the shoddy availability this past week. We’ve started the process of transitioning to a new host. This is a complicated process, and it’s not one we’ve done before, so I can’t say for sure how long it’ll take us. But we are working on it. Thanks for your patience as we’ve worked through this.