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.

src/voice/layerManifest.js

@@ -462,6 +462,7 @@ export const VOICE_OFF_LAYERS = Object.freeze({
   news: 'browsed in the News panel; voice tools are a later step',
   'wildlife-sightings':
     'community observation layer; no room in the prompt budget',
+  rail: 'train layer; no room in the prompt budget, and "trains" still names transit',
 });
 
 const TYPE_NAMES = Object.freeze({