feat(rail): add a Rail layer with keyless live trains

Live trains from 30 keyless operator feeds: GPS positions from 29 and
Irish Rail's station reports, shown as the operators publish them. 28
work out of the box; Renfe long and medium distance and KTMB appear once
their pack is built, because their vehicles name no route.

Packs are opt-in (scripts/build-rail-paths.mjs): the operator's own
route lines, stop names, next stops and trip-update delays for live
trains. Nothing downloads when the app starts, no train is placed from a
timetable, and no request carries a deployer's key.

server/providers/local.js

@@ -16,6 +16,7 @@ import { radioBrowserProxy } from './radio.js';
 import { gbfsProxy } from './gbfs.js';
 import { localReceiversProxy } from './local-receivers.js';
 import { transitProxy } from './transit.js';
+import { railProxy } from './rail.js';
 import { adsbLolProxy } from './aircraft/adsb-lol.js';
 import { aisLiveProxy } from './vessels/ais-live.js';
 import { trackBackfillProxies } from './aircraft/tracks.js';
@@ -71,6 +72,7 @@ function localProviderPlugins({
     gbfsProxy(),
     localReceiversProxy(),
     transitProxy(),
+    railProxy(),
     adsbLolProxy(),
     aisLiveProxy(),
     trackBackfillProxies(),