feat(transit): add Lisbon's Carris Metropolitana buses

Keyless GTFS-Realtime feed from Carris Metropolitana, documented in the
operator's public API repository. No licence is stated for the realtime
endpoint (the static GTFS is CC BY 4.0), so it is credited as a courtesy on
the same basis as the Metro Transit and OVapi feeds. The feed publishes km/h,
so a new `speedUnit` registry field lets the proxy convert to m/s. Route ids
wrap the GTFS route id in an area prefix and are read as the line number.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/CURRENT-STATE.md

@@ -4644,9 +4644,9 @@ Transit is off by default, and share links use token `j`. The movement panel ord
 places Transit directly after Street Traffic and before Bike Share. Cameras and
 utilities retain their own groups. The layer polls
 registered feeds near the camera every 15 seconds, below a 3,000 km altitude
-gate. Eighteen keyless regions are available: Boston, Austin, Minneapolis–St Paul,
+gate. Nineteen keyless regions are available: Boston, Austin, Minneapolis–St Paul,
 Helsinki, the Netherlands, Norway, South East Queensland, Rio de Janeiro
-(municipal buses and the Mobi-Rio BRT, two feeds), Szczecin, and nine in
+(municipal buses and the Mobi-Rio BRT, two feeds), Szczecin, the Lisbon Metropolitan Area, and nine in
 Ontario — Toronto (TTC surface vehicles; the subway publishes no
 positions), MiWay, Hamilton HSR, Durham Region, YRT/Viva, Guelph,
 Burlington, Barrie and Kingston. Mode silhouettes