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.

packages/types/src/freight/index.ts

@@ -497,6 +497,20 @@ export interface BookableSchedulesQuery {
   destinationYardId?: string;
 }
 
+export interface AvailableDaysQuery {
+  originYardId?: string;
+  destinationYardId?: string;
+}
+
+/**
+ * Day-level booking pool: the EAT calendar days that have at least one OPEN
+ * departure on a route. `days` are `yyyy-MM-dd` strings, e.g. `["2026-06-20"]`.
+ * No capacity is exposed — customers pick a day, not a train.
+ */
+export interface AvailableDaysResponse {
+  days: string[];
+}
+
 export interface BookableScheduleLocomotive {
   id: string;
   code: string;