feat(rust): the live map draws monuments by label, minor labels hidden (PLAN_REDESIGNS §4, D196)

A switch per monument label, a fleet default and a per-server override, on
Admin -> Rust visibility's live map card. Substations, caves, train tunnels,
wells and the other minor labels start hidden; every other label is drawn,
so a monument a game update adds appears. GET /map leaves hidden labels out
of the answer, so the website and the app both lose them.

No schema change: rows are map.marker.<label key> in rust_settings and
rust_map_overrides. No wire change.

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

server/router/admin/visibility.controller.js

@@ -42,6 +42,8 @@ async function describeMap() {
       const row = byId.get(s.id)
       return {
         ...sw,
+        // D196: the labels on this server's current map, one switch each.
+        markerLabels: map.markerLabels(map.monumentsOf(row)),
         name: s.name,
         enabled: Boolean(s.enabled),
         picture: row