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/data/railFeedsUsUrban.test.mjs

@@ -0,0 +1,57 @@
+// United States streetcar feeds (Seattle, Cincinnati): switched on with
+// their basis, polled for live positions, and sorted into categories with
+// the buses dropped.
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import {
+  RAIL_ENABLED_FEEDS,
+  classifyTrain,
+  getRailFeed,
+  getRegisteredRailFeed,
+  railFeedHasTripUpdates,
+  railFeedPositions,
+} from './railFeeds.js';
+
+// Licensed and switched on.
+const ON = ['seattle-streetcar', 'cincinnati-connector'];
+
+const TRAM = { category: 'transit', mode: 'tram' };
+
+const feed = (id) => getRegisteredRailFeed(id);
+const kind = (id, routeId, context) =>
+  classifyTrain(feed(id), routeId, context);
+
+test('the US streetcar feeds: licensed feeds on, each with its basis', () => {
+  for (const id of ON) {
+    assert.ok(getRailFeed(id), `${id} is pollable`);
+    assert.ok(RAIL_ENABLED_FEEDS.includes(feed(id)), id);
+    assert.ok(feed(id).terms.note, `${id} explains its basis`);
+    assert.ok(feed(id).staticGtfsUrl, `${id} has a timetable`);
+    assert.ok(feed(id).terms.quote, `${id} quotes its terms`);
+    // Nothing personal in the recorded basis.
+    assert.doesNotMatch(feed(id).terms.note, /@/, id);
+  }
+});
+
+test('the US streetcar feeds poll positions and trip updates', () => {
+  for (const id of ON) {
+    assert.equal(railFeedPositions(feed(id)), 'gps', id);
+    assert.ok(railFeedHasTripUpdates(feed(id)), id);
+  }
+});
+
+test('Seattle Streetcar: the two City of Seattle routes of the King County feed', () => {
+  assert.deepEqual(kind('seattle-streetcar', '100340'), TRAM);
+  assert.deepEqual(kind('seattle-streetcar', '102638'), TRAM);
+  assert.equal(kind('seattle-streetcar', '100001'), null, 'a Metro bus');
+  assert.equal(kind('seattle-streetcar', null), null);
+  assert.equal(
+    feed('seattle-streetcar').attribution,
+    'Transit scheduling, geographic, and real-time data provided by permission of King County',
+  );
+});
+
+test('Cincinnati Connector: the streetcar route, buses dropped', () => {
+  assert.deepEqual(kind('cincinnati-connector', '100'), TRAM);
+  assert.equal(kind('cincinnati-connector', '78'), null);
+});