remove route_calculation setting, always use OSRM routing (#1064)

The per-user route_calculation toggle was a second, hidden on/off layer
on top of the day footer's show-route button, and made it easy to end up
with straight-line routes for no obvious reason. Drop the setting
entirely: routing is always on, the footer toggle stays the single
switch. Old stored values are simply ignored (settings are key-value, no
migration needed).

client/src/pages/TripPlannerPage.tsx

@@ -830,7 +830,7 @@ export default function TripPlannerPage(): React.ReactElement | null {
               hasInspector={!!selectedPlace}
               hasDayDetail={!!showDayDetail && !selectedPlace}
               reservations={reservations}
-              showReservationStats={settings.route_calculation !== false}
+              showReservationStats={true}
               visibleConnectionIds={visibleConnections}
               onReservationClick={(rid) => {
                 const r = reservations.find(x => x.id === rid)