SELF_HOST.md references a 'Bull Queue Manager UI' that was removed with bull-board

[colinwilliams91]

Problem

SELF_HOST.md:86 currently instructs self-hosters:

You should be able to see the Bull Queue Manager UI on http://localhost:3002/admin/@/queues.

This is stale:

1. Bull-board was removed in commits c344bc0 cleanup: remove bull-board due to build errs it causes and 003fb21 cleanup: remove log for bull-board. The bull-board package is no longer in apps/api/package.json.
2. The route GET /admin/@/queues (apps/api/src/routes/admin.ts:26 -> queuesController in apps/api/src/controllers/v0/admin/queue.ts:68) returns JSON {webScraperActive, noActiveJobs}, not a UI. Hitting that URL does not render a "Manager UI."
3. README.md:22 explicitly says: "Posthog, supabase, stripe, langchain, logsnag, sentry, bullboard, and several other deps from the package.json are removed."

So the self-hoster following SELF_HOST.md will be confused: the documented Bull UI doesn't render.

Suggested fixes (whichever the maintainers prefer)

1. Restore bull-board if there's appetite (commit history says it was removed due to build errors -- those may be resolvable with a newer version), OR
2. Update SELF_HOST.md:86 to describe what /admin/@/queues actually returns (the JSON {webScraperActive, noActiveJobs} health endpoint) and drop the "Manager UI" framing, OR
3. Remove the line if the JSON endpoint isn't worth documenting either.

Out of scope for the cron-workflow PR (#50); filing separately so it can be triaged on its own merits.