feat(roadtrip): show every change to a road trip live to everyone on it

Two people shaping one drive were each editing their own copy: a via dragged on
one screen reached the other only on the next reload, and the route it changed
looked settled until then. Every write in the domain now announces itself over
the websocket the rest of the trip already uses — the five REST routes and the
matching MCP tools alike, so an assistant moving a stop is as visible as a
person doing it.

Two new trip-scoped events carry it: roadtripVia:changed with the day's whole
via list, and roadtripTrack:changed. The whole list rather than a delta, because
a via is identified by its position in a chain and a delta protocol would need
an ordering guarantee to be worth anything.

The originating socket is excluded through the X-Socket-Id header the other
domains already forward, so nobody watches their own change arrive twice.

client/src/api/wsEventPolicy.ts

@@ -30,6 +30,11 @@ export const HANDLED_OUTSIDE_TRIP_STORE = [
   'collab:message:created',
   'collab:message:reacted',
   'collab:message:deleted',
+  // Road trip shaping — components/Roadtrip/useRoadtripVias. The points a drive is
+  // routed through live in that hook and nowhere else; a store slice for them would be a
+  // second copy of the same list to keep in step.
+  'roadtripVia:changed',
+  'roadtripTrack:changed',
   // In-app notifications — hooks/useInAppNotificationListener
   'notification:new',
   'notification:updated',