add yard distances management to rule engine

- Introduced new yard distances resource with CRUD operations.
- Created migration for yard distances table with necessary constraints.
- Implemented service and repository for yard distances handling.
- Added controller for API endpoints to manage yard distances.
- Updated rule engine configuration to include yard distances.
- Enhanced rule engine resource page to support yard distance selection.
- Updated contracts and train builder pages to handle new yard distance logic.
- Added error handling utility for better error message extraction.

apps/edr-freight-api/src/modules/rule-engine/entities/yard-distance.entity.ts

@@ -0,0 +1,35 @@
+import { BaseEntity } from '@edr/api-common';
+import { Column, Entity, Index, JoinColumn, ManyToOne } from 'typeorm';
+
+import { Yard } from './yard.entity';
+
+/**
+ * Configured rail distance between two yards. Route creation reads segment
+ * kilometres from here (symmetric: A→B serves B→A too) instead of taking
+ * them as free-text input — see RoutesService.validateMilestones.
+ *
+ * Uniqueness on (from_yard_id, to_yard_id) is a partial index in the DB
+ * (WHERE deleted_at IS NULL) rather than a @Unique decorator, so a
+ * soft-deleted pair can be re-created.
+ */
+@Entity({ schema: 'freight', name: 'yard_distances' })
+@Index(['fromYardId'])
+@Index(['toYardId'])
+export class YardDistance extends BaseEntity {
+  @Column({ name: 'from_yard_id', type: 'uuid' })
+  fromYardId!: string;
+
+  @ManyToOne(() => Yard)
+  @JoinColumn({ name: 'from_yard_id' })
+  fromYard?: Yard;
+
+  @Column({ name: 'to_yard_id', type: 'uuid' })
+  toYardId!: string;
+
+  @ManyToOne(() => Yard)
+  @JoinColumn({ name: 'to_yard_id' })
+  toYard?: Yard;
+
+  @Column({ name: 'distance_km', type: 'decimal', precision: 10, scale: 2 })
+  distanceKm!: string; // decimal columns come back as string in typeorm/pg — keep consistent with RouteMilestone.distanceKm
+}