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/dto/available-days-query.dto.ts

@@ -0,0 +1,14 @@
+import { ApiPropertyOptional } from '@nestjs/swagger';
+import { IsOptional, IsUUID } from 'class-validator';
+
+export class AvailableDaysQueryDto {
+  @ApiPropertyOptional({ format: 'uuid' })
+  @IsOptional()
+  @IsUUID()
+  originYardId?: string;
+
+  @ApiPropertyOptional({ format: 'uuid' })
+  @IsOptional()
+  @IsUUID()
+  destinationYardId?: string;
+}