feat(train-scheduling): numbered marshalling-doc picker per corridor stop

Backend now generates a separate marshalling document per corridor stop
where the consist actually coupled/uncoupled/switched something
(marshallingStops/marshallingDocumentAt), instead of one 'current
position' doc. Wires that into the backoffice:

- TrainScheduleV2DetailPage: the single Intercity Marshalling menu item
  becomes one item per stop with a logged change, falling back to the
  old single item when nothing has happened yet.
- TrainScheduleTrackPage: same fallback/menu treatment on its own
  marshalling button.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/edr-freight-web/backoffice/src/services/api.ts

@@ -85,6 +85,7 @@ import type {
   UpdateCheckpointPayload,
   DispatchSchedulePayload,
   StaffBookingWindow,
+  MarshallingStop,
   ScheduleMergePreview,
   TrainScheduleDetail,
   TrainScheduleFilters,
@@ -595,6 +596,13 @@ export const api = {
       ({ id }) => QUERY_KEYS.TRAIN_SCHEDULING.track(id),
     ),
 
+    marshallingStops: endpoint<{ id: string }, MarshallingStop[]>(
+      "train-scheduling",
+      "marshalling-stops",
+      ({ id }) => trainSchedulingService.getMarshallingStops(id),
+      ({ id }) => QUERY_KEYS.TRAIN_SCHEDULING.marshallingStops(id),
+    ),
+
     unassignedBookings: endpoint<
       { scheduleId: string },
       UnassignedBookingsResponse

apps/edr-freight-web/backoffice/src/services/trainScheduling.service.ts

@@ -33,6 +33,7 @@ import type {
   UpdateCheckpointPayload,
   DispatchSchedulePayload,
   StaffBookingWindow,
+  MarshallingStop,
   ScheduleMergePreview,
   TrainScheduleDetail,
   UpdateScheduleWindowRulePayload,
@@ -760,6 +761,24 @@ export const trainSchedulingService = {
     return response.data;
   },
 
+  getMarshallingStops: async (scheduleId: string): Promise<MarshallingStop[]> => {
+    const response = await client.get<MarshallingStop[]>(
+      URL_CONSTANTS.TRAIN_SCHEDULING.MARSHALLING_STOPS(scheduleId),
+    );
+    return unwrap(response.data);
+  },
+
+  downloadMarshallingDocumentAt: async (
+    scheduleId: string,
+    stopIndex: number,
+  ): Promise<Blob> => {
+    const response = await client.get(
+      URL_CONSTANTS.TRAIN_SCHEDULING.MARSHALLING_DOCUMENT_AT(scheduleId, stopIndex),
+      { responseType: "blob" },
+    );
+    return response.data;
+  },
+
   getTrack: async (scheduleId: string): Promise<TrainTrackResponse> => {
     const response = await client.get<TrainTrackResponse>(
       URL_CONSTANTS.TRAIN_SCHEDULING.CHECKPOINTS(scheduleId),