feat(cockpit): an application can add its own cockpit subjects; the Rail and Transit layers expose the read and hold APIs such a subject needs

GEV itself registers no new subject: with no provider, the Cockpit offers
aircraft, satellites and vessels as before, except that the most recently
selected of them now wins entry.

- services.cockpitSubjects: providers ({kind, layerId, entryFace, priority,
  isEntryAllowed, read, hold, release, hud}) are checked once by the
  coordinator; frames and HUD views on every update; a throwing provider
  ends its view or keeps the last HUD.
- Entry: the most recently selected subject wins, across all kinds.
- Camera: a frame may turn the ground clamp off, anchor exactly on the
  subject and update every frame.
- A generic HUD: kicker, title, cards, always-visible source rows, banner,
  a veil with light streaks (off under reduced motion) and a bottom
  progress line whose close ticks merge.
- Text comes from the provider, already in the page's language
  (./i18n/locale: getLocale, onLocaleChange).
- Rail and Transit read and hold APIs (getSelectedTrain/Vehicle,
  getCockpitSubject, setCockpitSubject, focusTrain/Vehicle); a held
  train's marker, card and route line are hidden, and its feed keeps
  polling while held.
- ./layers/rail/paths is exported.

scripts/format-scope.json

@@ -1422,5 +1422,15 @@
   "src/ui/ownerFlagSheet.js",
   "src/data/placePacksLoading.test.mjs",
   "src/ui/placePacksLoading.js",
-  "src/ui/placePacksLoading.test.mjs"
+  "src/ui/placePacksLoading.test.mjs",
+  "src/cockpitSubjectProviders.js",
+  "src/cockpitSubjectProviders.test.mjs",
+  "src/cockpitProgress.js",
+  "src/cockpitProgress.test.mjs",
+  "src/i18n/hostLocale.js",
+  "src/ui/cockpitSubjectView.test.mjs",
+  "src/ui/styles/cockpitSubject.css",
+  "src/layers/rail/cockpitSubject.js",
+  "src/layers/rail/cockpitSubject.test.mjs",
+  "src/layers/transit/cockpitSubject.js"
 ]