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-api/src/modules/train-scheduling/train-capacity.util.ts

@@ -69,6 +69,25 @@ export function deriveTrainCapacityFromLocomotive(
 export const MAX_FALLBACK_WEIGHT = 3500;
 export const MAX_FALLBACK_LENGTH = 760;
 
+/**
+ * Effective pull limits for a train set with multiple locomotives: the weakest
+ * locomotive caps the train, so take the minimum pull weight and minimum length
+ * across all assigned locomotives. Returns null when no locomotives are given.
+ */
+export function minLocomotiveLimits(
+  locomotives: Array<Pick<LocomotiveLimits, 'maxPullWeightTons' | 'maxTrainLengthMeters'>>,
+): LocomotiveLimits | null {
+  if (!locomotives.length) return null;
+  return {
+    maxPullWeightTons: Math.min(
+      ...locomotives.map((l) => Number(l.maxPullWeightTons) || Infinity),
+    ),
+    maxTrainLengthMeters: Math.min(
+      ...locomotives.map((l) => Number(l.maxTrainLengthMeters) || Infinity),
+    ),
+  };
+}
+
 /** Per-booking train length from wagon count and freight-specific wagon type length. */
 export function bookingTrainLengthMeters(
   freightType: string | null | undefined,