feat(train-scheduling): mid-route consist changes, audit history, safer workspace

- planned couples: loose wagons join the train at a route stop, added
  from the schedule yards tab; capacity credits them per corridor edge
  and coupling validates locomotive weight/length caps per leg
- real-cut toggle: a cut wagon permanently leaves the train build at
  its cut yard (soft cut still sits out one trip only)
- fix heaviest-leg display counting a shared slot's full cargo on
  every spanned edge (phantom pull-weight overload on S-2026-00045)
- confirmation dialogs for workspace add/load/unload/remove actions
- train-builder History and Detached-wagons tabs, backed by paginated
  endpoints; builder detaches now always write adjustment-log rows

Migrations 3660 (planned_wagon_couples, planned_wagon_real_cuts) and
3670 (adjustment log train_schedule_id nullable) — both applied to the
dev DB by hand; watch mode does not run migrations.

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

apps/edr-freight-api/src/modules/train-schedules/entities/schedule-wagon-adjustment-log.entity.ts

@@ -17,8 +17,9 @@ export type WagonAdjustmentAction = (typeof WAGON_ADJUSTMENT_ACTIONS)[number];
 @Index(['trainScheduleId'])
 @Index(['trainId'])
 export class ScheduleWagonAdjustmentLog extends BaseEntity {
-  @Column({ name: 'train_schedule_id', type: 'uuid' })
-  trainScheduleId!: string;
+  /** Null when the change was made from the train builder with no live schedule. */
+  @Column({ name: 'train_schedule_id', type: 'uuid', nullable: true })
+  trainScheduleId!: string | null;
 
   @Column({ name: 'train_id', type: 'uuid' })
   trainId!: string;