feat(train-sets): implement multi-locomotive support for train sets

- Added TrainSetLocomotive entity to link multiple locomotives to a train set.
- Updated TrainSet entity to include a OneToMany relationship with TrainSetLocomotive.
- Modified the train scheduling logic to require at least two locomotives for a train set.
- Enhanced the UI components to support selecting multiple locomotives.
- Introduced new permissions for viewing customs clearance.
- Updated migrations to create the train_set_locomotives table and backfill existing data.
- Implemented utility functions for managing train numbers based on cargo type and direction.
- Added tests for train number utilities to ensure correct functionality.

apps/edr-freight-web/backoffice/src/components/trainScheduling/AllocateBookingWizard.tsx

@@ -8,6 +8,7 @@ import {
   Checkbox,
   Group,
   Modal,
+  MultiSelect,
   Paper,
   Radio,
   RingProgress,
@@ -107,7 +108,7 @@ export function AllocateBookingWizard({
   const [selectedScheduleId, setSelectedScheduleId] = useState<string | null>(null);
   const [routeId, setRouteId] = useState("");
   const scheduleDate = booking.scheduledDate;
-  const [locomotiveId, setLocomotiveId] = useState("");
+  const [locomotiveIds, setLocomotiveIds] = useState<string[]>([]);
   const [extraBookingIds, setExtraBookingIds] = useState<string[]>([]);
   const [forceAssign, setForceAssign] = useState(false);
   const [previewResult, setPreviewResult] = useState<TrainSchedulePreviewResponse | null>(null);
@@ -152,7 +153,7 @@ export function AllocateBookingWizard({
 
   useEffect(() => {
     if (scheduleMode === "new") {
-      setLocomotiveId("");
+      setLocomotiveIds([]);
     }
   }, [routeId, scheduleMode]);
 
@@ -264,11 +265,11 @@ export function AllocateBookingWizard({
 
   const ensureSchedule = async (): Promise<string> => {
     if (scheduleMode === "existing" && selectedScheduleId) return selectedScheduleId;
-    if (!routeId || !scheduleDate || !locomotiveId) {
-      throw new Error("Select route, date, and locomotive");
+    if (!routeId || !scheduleDate || locomotiveIds.length < 2) {
+      throw new Error("Select route, date, and at least two locomotives");
     }
     const created = await create.mutateAsync({
-      payload: { routeId, scheduleDate, locomotiveId },
+      payload: { routeId, scheduleDate, locomotiveIds },
     });
     setSelectedScheduleId(created.id);
     return created.id;
@@ -526,17 +527,25 @@ export function AllocateBookingWizard({
                     onChange={(v) => setRouteId(v ?? "")}
                     searchable
                   />
-                  <Select
-                    label="Locomotive"
-                    placeholder={routeId ? "Select locomotive" : "Select a route first"}
+                  <MultiSelect
+                    label="Locomotives"
+                    description="At least two (front and back)"
+                    placeholder={
+                      routeId ? "Select at least two locomotives" : "Select a route first"
+                    }
                     data={(locomotivesQuery.data ?? []).map((l) => ({
                       value: l.id,
                       label: `${l.code}${l.name ? ` · ${l.name}` : ""}`,
                     }))}
-                    value={locomotiveId || null}
-                    onChange={(v) => setLocomotiveId(v ?? "")}
+                    value={locomotiveIds}
+                    onChange={setLocomotiveIds}
                     searchable
                     disabled={!routeId}
+                    error={
+                      locomotiveIds.length > 0 && locomotiveIds.length < 2
+                        ? "Select at least two locomotives"
+                        : undefined
+                    }
                     nothingFoundMessage={
                       routeId ? "No available locomotives for this corridor" : "Select a route first"
                     }