Expose #job-board via an API

[vcarl]

This interacts with the reactiflux.com repo, messages posted that don't meet our validation requirements are not removed from the /jobs page. This is very much not ideal and limits our usefulness as a job space, because spammy and duplicate postings remain.

We should replace the current system with a reflection of the currently-active posts in the server. We monitor as far back as 90 days, with skill ads (forhire posts) kept up for several days.

I'm thinking the simplest way to do this would be to set up a Cloudflare Worker with a KV store to track posts. Since we scan the channel for posts on startup, the lack of persistence isn't a problem. Then, on the website, we can read the list of posts and present a similar experience. Long-term, it would be nice to improve the experience, and maybe consider presenting a list of skill ads that are currently active.

[vcarl]

At first I thought we'd need to set up a database for this, but actually I guess not? It's all stored in memory, scanning history for active posts. Maybe it'll make sense to parse further back into history on startup, so we can give more than a single week's backlog, but I don't know that a full-ass database is the way to go there.

[vcarl]

Shipped in #439