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/train-scheduling.controller.ts

@@ -32,6 +32,7 @@ import { PreviewTrainScheduleDto } from "./dto/preview-train-schedule.dto";
 import { RecordCheckpointDto } from "./dto/record-checkpoint.dto";
 import { AvailableLocomotivesQueryDto } from "./dto/available-locomotives-query.dto";
 import { BookableSchedulesQueryDto } from "./dto/bookable-schedules-query.dto";
+import { AvailableDaysQueryDto } from "./dto/available-days-query.dto";
 import { UpdateTrainSchedulingGlobalRulesDto } from "./dto/update-train-scheduling-global-rules.dto";
 import { TrainSchedulingService } from "./train-scheduling.service";
 import { BookingBatchService } from "./booking-batch.service";
@@ -108,6 +109,20 @@ export class TrainSchedulingController {
     );
   }
 
+  @Get("available-days")
+  // No staff guard: customers hit this while creating a booking to find which
+  // DAYS have a departure on their route. Day-level pooling — no capacity is
+  // returned, only the list of bookable days.
+  @ApiOperation({
+    summary: "Distinct days with an OPEN same-route departure (day-level pool)",
+  })
+  getAvailableDays(@Query() query: AvailableDaysQueryDto) {
+    return this.trainSchedulingService.getAvailableDays(
+      query.originYardId,
+      query.destinationYardId,
+    );
+  }
+
   @Get("container/eligible-bookings")
   @TrainSchedulingView()
   @ApiOperation({ summary: "List eligible container bookings" })