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-scheduling/wagon-plan-flex.util.ts

@@ -54,6 +54,13 @@ export type WagonStock = {
    * math.
    */
   byYardId?: Map<string, Map<string, number>>;
+  /**
+   * Wagons the schedule CUTS mid-route (staff plan): each is stock only up to
+   * its cut stop. Consumers debit it from its pool on every edge at/after the
+   * cut, so a leg riding past the cut never counts it. Absent = no cuts.
+   * `poolYardId` is the wagon's boarding pool ('' on a single-yard consist).
+   */
+  cutWagons?: Array<{ wagonTypeId: string; poolYardId: string; cutYardId: string }>;
 };
 
 export type FlexPlanResult = {
@@ -324,6 +331,16 @@ export function planWagonsWithStock(params: {
     }
     return row;
   };
+  // Cut wagons are pre-consumed on every edge at/after their cut stop: they
+  // are steel for gmp→lebu but not for gmp→dct. Unknown cut yard (no stops
+  // given / off-corridor) is skipped — conservative, same as before cuts.
+  for (const cut of stock.cutWagons ?? []) {
+    const fromEdge = stops.indexOf(cut.cutYardId);
+    if (fromEdge < 0) continue;
+    const pool = stock.byYardId ? cut.poolYardId : '';
+    const row = usedRow(rowKeyFor(cut.wagonTypeId, pool));
+    for (let e = fromEdge; e < edgeCount; e += 1) row[e] += 1;
+  }
   const availableFor = (wagonTypeId: string, leg: BookingLeg): number => {
     const pool = poolOf(leg);
     const total = totalFor(wagonTypeId, pool);