feat(train-crew): implement crew assignment functionality

- Added TrainCrewAssignment module with controller and service for managing crew assignments.
- Integrated TrainCrewAssignmentService into TrainSchedulingService to ensure crew readiness before train dispatch.
- Updated TrainScheduling module to include TrainCrewModule for dependency injection.
- Introduced new permissions for assigning train crew in freight permissions registry.
- Enhanced front-end ScheduleCrewPage to allow assignment of crew members to train schedules, including validation and UI for adding/removing drivers and support crew.
- Created trainCrewAssignment.service to handle API interactions for crew assignments.

apps/edr-freight-api/src/modules/train-crew/entities/train-crew-assignment.entity.ts

@@ -0,0 +1,114 @@
+import { Column, Entity, Index, JoinColumn, ManyToOne } from 'typeorm';
+import { BaseEntity } from '@edr/api-common';
+
+import { TrainCrewMember, TrainCrewRole } from './train-crew-member.entity';
+
+/**
+ * Legacy fixed corridor segments.
+ *
+ * Kept only so historic rows written before segments became yard-to-yard still
+ * read back. New assignments carry `fromYardId`/`toYardId` instead: staff pick
+ * any two yards on the corridor, so a leg is no longer limited to the three
+ * spans the original design hard-coded.
+ */
+export enum CrewSegment {
+  INDODE_DIRE_DAWA = 'INDODE_DIRE_DAWA',
+  DIRE_DAWA_NAGAD = 'DIRE_DAWA_NAGAD',
+  FULL_CORRIDOR = 'FULL_CORRIDOR',
+}
+
+/** Driver duty role for one run (§2). Null for non-driving crew. */
+export enum CrewDutyRole {
+  PRIMARY = 'PRIMARY',
+  ASSISTANT = 'ASSISTANT',
+  BENCH_RELIEF = 'BENCH_RELIEF',
+}
+
+export enum CrewAssignmentStatus {
+  PLANNED = 'PLANNED',
+  CONFIRMED = 'CONFIRMED',
+  COMPLETED = 'COMPLETED',
+  REMOVED = 'REMOVED',
+}
+
+/**
+ * One roster member assigned to one train schedule.
+ *
+ * `role` is snapshotted from the roster at assignment time: a member who later
+ * changes role must not silently rewrite the crew of a run that already
+ * departed. `dutyRole` and `segment` live here rather than on the roster
+ * because they are properties of THIS run — a driver who is Primary on one
+ * trip is Assistant on the next. Crew sizes are free-form: operations size each
+ * run to its own need rather than to a fixed pairing case.
+ *
+ * Duty stamps feed the §3 monthly overtime totals. Per the agreed scope the
+ * platform reports OT hours only; no salary is stored anywhere, and the payroll
+ * conversion stays with finance.
+ */
+@Entity({ schema: 'freight', name: 'train_crew_assignments' })
+@Index(['trainScheduleId'])
+@Index(['crewMemberId'])
+@Index(['status'])
+export class TrainCrewAssignment extends BaseEntity {
+  @Column({ name: 'train_schedule_id', type: 'uuid' })
+  trainScheduleId!: string;
+
+  @Column({ name: 'crew_member_id', type: 'uuid' })
+  crewMemberId!: string;
+
+  @ManyToOne(() => TrainCrewMember, { onDelete: 'RESTRICT' })
+  @JoinColumn({ name: 'crew_member_id' })
+  crewMember?: TrainCrewMember;
+
+  @Column({ name: 'role', type: 'varchar', length: 32 })
+  role!: TrainCrewRole;
+
+  @Column({ name: 'duty_role', type: 'varchar', length: 16, nullable: true })
+  dutyRole?: CrewDutyRole | null;
+
+  /** Legacy fixed segment — null on every assignment written since yard legs. */
+  @Column({ name: 'segment', type: 'varchar', length: 24, nullable: true })
+  segment?: CrewSegment | null;
+
+  /**
+   * The leg this driver works, as two yards on the corridor.
+   *
+   * Free-form on purpose: operations pick any yard as a handover point, so a
+   * crew change at Meiso or Feto is expressible without a code change. The
+   * schedule's own origin and destination bound what staff may choose.
+   */
+  @Column({ name: 'from_yard_id', type: 'uuid', nullable: true })
+  fromYardId?: string | null;
+
+  @Column({ name: 'to_yard_id', type: 'uuid', nullable: true })
+  toYardId?: string | null;
+
+  /**
+   * Mandatory off-duty layover at Dire Dawa (§1.3). The document gives ~5 hours
+   * as a typical duration, not a rule, so nothing here enforces a length — the
+   * stamps are recorded and reported.
+   */
+  @Column({ name: 'layover_start_at', type: 'timestamptz', nullable: true })
+  layoverStartAt?: Date | null;
+
+  @Column({ name: 'layover_end_at', type: 'timestamptz', nullable: true })
+  layoverEndAt?: Date | null;
+
+  /** Worked span for this run — accumulated monthly for the §3 OT calculation. */
+  @Column({ name: 'duty_start_at', type: 'timestamptz', nullable: true })
+  dutyStartAt?: Date | null;
+
+  @Column({ name: 'duty_end_at', type: 'timestamptz', nullable: true })
+  dutyEndAt?: Date | null;
+
+  @Column({
+    name: 'status',
+    type: 'varchar',
+    length: 16,
+    default: CrewAssignmentStatus.PLANNED,
+  })
+  status!: CrewAssignmentStatus;
+
+  @Column({ name: 'notes', type: 'text', nullable: true })
+  notes?: string | null;
+}