feat(train-scheduling): implement day-level booking pool

- Added `unplaced` method in `BookingNotifierService` to log warnings for bookings that cannot be placed on any train.
- Introduced `getAvailableDays` method in `TrainSchedulingService` to retrieve distinct days with open departures for a given route.
- Created `AvailableDaysQueryDto` for querying available days based on origin and destination yards.
- Updated `TrainSchedulingController` to expose an endpoint for available days.
- Modified frontend components to support day-level booking, allowing customers to select only a day without pinning to a specific train.
- Removed references to train schedules in booking forms and review steps, emphasizing day selection.
- Added a database migration to create an index for efficient querying of bookings by route and day.

apps/edr-freight-api/src/modules/train-scheduling/booking-notifier.service.ts

@@ -67,6 +67,17 @@ export class BookingNotifierService {
     );
   }
 
+  /**
+   * Staff-facing warning when a pooled booking fits no train on its chosen day.
+   * It stays pending and is retried next batch; staff can add capacity or pin it
+   * to a train manually. Mirrors {@link scheduleFull} — no customer notification.
+   */
+  unplaced(b: Booking, day: string): void {
+    this.logger.warn(
+      `UNPLACED — ${this.ref(b)} could not be placed on any train for ${day}; add capacity or assign it manually.`,
+    );
+  }
+
   displaced(b: Booking): void {
     const msg = `Booking ${b.reference ?? b.id} was displaced by a government booking. Move to another schedule or cancel.`;
     void this.notifyContact(b, msg, 'DISPLACED');