fix(rust): nothing names who is online by default

The org lead's rule, settled 2026-09-22: who is online is always the
narrowest audience - staff - unless an operator deliberately widens it,
and a count is fine where a list of names is not.

The public site broke that in three places since phase 4. The Online
tab named every player, the feed carried joins, respawns, deaths, chat
and tallies, and the leaderboard's lastSeen - refreshed every minute by
a gather tally - said who was on as plainly as either. All three now
sit behind one setting:

* PRESENCE_KINDS, a subset of the public allowlist, gated per request.
  Below the audience the feed keeps the server's own story (wipe, start,
  shutdown) and says presenceHidden rather than looking quiet.
* the Online route answers { players: [], hidden, count, audience } -
  same shape, so an older client renders empty rather than breaking.
* rungs staff / signed_in / public, fleet-wide default in a new
  rust_settings table with an optional per-server override on
  rust_servers; an unknown stored word narrows to staff.
* the viewer's standing is RE-READ from the users row (ctx.users.getById),
  not taken from the token, so a demotion or a ban applies on the next
  request. Walked: a moderator demoted mid-session lost the roll call on
  the same cookie.
* per-viewer answers are Cache-Control: private, no-store.
* GET/PUT /admin/rust/visibility (requireRole admin) and an admin page,
  Rust visibility; every save is one activity-log row.

The browser walk also found every empty state in this module rendering
as a blank box. Core's EmptyState renders children only; this module
passed title/message (the shape the Integration Kit template teaches)
and React dropped both without a word. Fixed module-side with a small
Empty wrapper - nothing core or module-uo renders changes - and a client
test that refuses a titled EmptyState or a PageHeader subtitle.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

server/core.js

@@ -86,6 +86,14 @@ module.exports = {
   // that needs an identity needs to *read* one.
   auth: { getUserFromRequest: (...args) => need().auth.getUserFromRequest(...args) },
 
+  // One user by id (MODULE_API.md §2.3, 1.1.0). Here for the presence gate
+  // (`model/visibility`): `getUserFromRequest` decodes a token and nothing more,
+  // so the role in it is the role the account had when the token was minted. A
+  // moderator demoted this morning would keep reading who is online until their
+  // token expired. Re-reading the row is what makes a demotion — or a ban — take
+  // effect on the next request, the same promise core's admin tier makes.
+  users: { getById: (...args) => need().users.getById(...args) },
+
   // Core's middleware, taken as values rather than wrapped: express stores the
   // function reference at mount time, so a wrapper is what would end up in the
   // stack. Routers are built inside `register()`, so `ctx` is set by then.