feat: add wagon usage computation and maintenance logging features

- Implemented  utility to calculate wagon usage metrics for train schedules.
- Created  for sending wagons to maintenance with optional notes.
- Added unit tests for train builder maintenance functionalities, including formatting train run labels and building maintenance notes.
- Developed  component for merging train schedules with detailed previews and reasons for merging.
- Introduced  component for selecting wagons with search functionality and selection limits.
- Created  for displaying and filtering audit logs, including detailed views of individual log entries.
- Added  for handling API interactions related to audit logs, including fetching logs and entity types.

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

@@ -29,6 +29,7 @@ import type {
   PinWagonsPayload,
   RecordCheckpointPayload,
   StaffBookingWindow,
+  ScheduleMergePreview,
   TrainScheduleDetail,
   UpdateScheduleWindowRulePayload,
   TrainScheduleFilters,
@@ -294,6 +295,29 @@ export const trainSchedulingService = {
     return unwrap(response.data);
   },
 
+  /** What a merge would do — drives the confirmation modal. Read-only. */
+  previewScheduleMerge: async (
+    scheduleId: string,
+    targetTrainId: string,
+  ): Promise<ScheduleMergePreview> => {
+    const response = await client.get<ScheduleMergePreview>(
+      URL_CONSTANTS.TRAIN_SCHEDULING.MERGE_PREVIEW(scheduleId, targetTrainId),
+    );
+    return unwrap(response.data);
+  },
+
+  /** Merge another train into this schedule. This schedule always survives. */
+  mergeScheduleTrain: async (
+    scheduleId: string,
+    payload: { targetTrainId: string; reason?: string },
+  ): Promise<TrainScheduleDetail> => {
+    const response = await client.post<TrainScheduleDetail>(
+      URL_CONSTANTS.TRAIN_SCHEDULING.MERGE_TRAIN(scheduleId),
+      payload,
+    );
+    return unwrap(response.data);
+  },
+
   markBookingPaid: async (bookingId: string): Promise<void> => {
     await client.post(
       URL_CONSTANTS.TRAIN_SCHEDULING.MARK_BOOKING_PAID(bookingId),