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.

README.md

@@ -446,6 +446,7 @@ Twenty-three layers and map sources. **Twenty-one have a keyless path.** Some of
 | 📷 **Street Level**         | Street-level photos behind one panel, one chip per provider: coverage on the streets, image cones, an embedded viewer with full-screen **EXPAND**. Mapillary, Google Street View, KartaView and Panoramax | Mapillary · Google · KartaView · Panoramax | 🟢 KartaView, Panoramax · 🟡 Mapillary token · 🔴 Google Maps key |
 | 📻 **Radio**                | Geolocated world radio with an **analog tuner** — drag the needle across up to 750 stations and the globe flies to each broadcaster                                                                                                                                                                                                                                                 | Radio Browser / broadcasters            | 🟢                                                                                                  |
 | 🚌 **Transit**              | Live buses, trams, metros, trains and ferries with delayed playback between reports, selected-vehicle trails, and mode-coloured DETECT labels — Boston, Austin, Minneapolis, Helsinki, the Netherlands, Norway, South East Queensland, Rio de Janeiro (buses and BRT), Szczecin, Lisbon (Carris Metropolitana and the city’s Carris), Prague, Warsaw, Kraków, Poznań, Gdańsk, Rzeszów, Vilnius, Bucharest, Cluj-Napoca, Iași, Rome, Turin, Venice (buses and waterbuses), Bordeaux, Montpellier, Rouen, Toulon, Le Havre, Tours, Málaga, Sendai, Johor Bahru, Kota Bharu, Adelaide, Atlanta, Denver, Edmonton, Halifax, Victoria, and nine in Ontario: Toronto (surface vehicles; the subway publishes no positions), Mississauga, Hamilton, Durham Region, York Region, Guelph, Burlington, Barrie and Kingston                                                                                                                                               | Operator GTFS-Realtime feeds            | 🟢                                                                                                  |
+| 🚆 **Rail**                 | Live trains across the US, Canada, Australia, Ireland, Finland, Spain, Norway, Malaysia, Japan and France, from 30 keyless operator feeds: live GPS positions from 29 of them and Irish Rail’s station reports, 28 live out of the box, and Renfe long and medium distance and KTMB once their pack is built. No train is placed from a timetable. Opt-in packs (`node scripts/build-rail-paths.mjs --feed <id>` or `--all`) add the operator’s own route lines, stop names, next stops and trip-update delays. Coloured by service category (urban, local, regional, national, international) with a filter chip and legend for each; trains are drawn once when several feeds carry them, and open a card per train. Buses in mixed feeds are dropped by the server                                                                                                                                                                                                                                                                                         | Operator GTFS-Realtime feeds (static GTFS for opt-in packs) | 🟢                                                                                                  |
 | 🚲 **Bikeshare**            | Live station availability                                                                                                                                                                                                                                                                                                                                                           | GBFS                                    | 🟢                                                                                                  |
 | 🧭 **Directions**           | Click A and B on the globe for a street-following drive, walk or cycle route draped on the terrain with turn-by-turn steps — then FLY the camera along it. No key, no geocoder, no mic                                                                                                                                                                                              | OSRM on FOSSGIS servers (OpenStreetMap) | 🟢                                                                                                  |
 | ⌖ **OSM Places**           | Voice place search ("hospitals in Kathmandu") from OpenStreetMap, drawn as numbered points that follow-up questions can filter. Needs your own Overpass server (`OVERPASS_UPSTREAMS`); off otherwise                                                                                                                                                                                                                                                                                                                               |