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.

.gitignore

@@ -14,6 +14,8 @@ qa-shots/
 output/
 .gev-logs/
 .gev-cache/
+# Local build output, e.g. rail path packs (scripts/build-rail-paths.mjs).
+.cache/
 # Browser QA gate evidence (screenshots, console and network dumps).
 qa-artifacts/
 # Playwright MCP session logs: browser consoles can carry tokens in URLs.