Linode, the company who owns the data center where the production instance of the Manager lives, has provided two updates so far:
Update - We have been experiencing a catastrophic DDoS attack which is being spread across hundreds of different IP addresses in rapid succession, making mitigation extremely difficult. We are currently working with our upstreams to implement more complete mitigation. Sep 4, 00:45 UTC
Unfortunately, given the nature of the attack, I have no access to the production host or any data.
Something like this occurred earlier this year, and Linode's response consistent and sustained and, eventually, they were able to put effective counter-measures in place and restore service. I expect that the same sort of thing is happening now, but all I can really do is wait.
Thanks again for using (or trying to use) the Manager!