Create endpoint with math worker status

[patcon]

Problem:
Math worker currently falls down quite often. This isn't knowable outside prod access, though shows up in "loading..." status for new convos, and would also manifest as convos and reports not updating realtime (though this is less obviously the case).

Suggested solution:
A /health API endpoint with a key for math worker status. E.g., https://microservices.io/patterns/observability/health-check-api.html

This would allow a status page to be created, and a better understanding of uptime for all users. (e.g., people expecting to launch a important convo might wish to do so during hours when math worker is less likely to have issues).

Alternative suggestions:

• get math worker to never fall over
• improve error output/handling of "loading..." screens and report/participation interface. Related: fix: show report errors in more cases #899

Additional context:
None. But this feels like a smaller task that could greatly improve the experience of first-time users.