Generalize per-vehicle-option booking rules to Front Seat too

Front Seat previously had a hardcoded max-per-booking check with no enable
toggle; now every Vehicle Option (front_seat/back_seat/whole_vehicle) gets
the same config-driven pair — an on/off toggle and a max passenger_count —
surfaced via new BOOKING_*_ENABLED/BOOKING_*_MAX_PER_BOOKING env vars,
editable from ManageAppSettings, and exposed on route pricing as
max_per_booking.

app-modules/routing/src/Http/Resources/RoutePricingResource.php

@@ -18,6 +18,7 @@ class RoutePricingResource extends JsonResource
             'vehicle_option' => $this->vehicle_option->value,
             'price' => (string) $this->price,
             'is_blocked' => $this->is_blocked,
+            'max_per_booking' => config("booking.{$this->vehicle_option->value}_max_per_booking"),
         ];
     }
 }