feat: Implement container hazardous-cargo surcharge logic

- Added support for container hazardous-cargo surcharge (HAZARDOUS billed PER_CONTAINER) in the rule engine.
- Introduced new method  in  to calculate and apply container hazard charges based on booking details.
- Updated  to handle per-container hazard rates, ensuring they are scoped by trade direction and lane.
- Enhanced tests to cover scenarios for container hazard rates, including validation for required fields and conflict checks.
- Created a migration to update existing rates and enforce new constraints for container hazard rates in the database.

apps/edr-freight-api/src/modules/rule-engine/entities/rate.entity.ts

@@ -88,6 +88,10 @@ export type RateAppliesTo = typeof RATE_APPLIES_TO[number];
  */
 export const RATE_TRIGGERS = [
   'ALWAYS',
+  // Hazardous cargo. Two shapes under one trigger, told apart by the unit:
+  // PER_CONTAINER is the container surcharge, sold per direction + lane and
+  // optionally per box size (20ft / 40ft) like the empty-return service;
+  // PER_TON is the bulk surcharge, direction-agnostic and unscoped.
   'HAZARDOUS',
   'OVERWEIGHT',
   'REEFER',
@@ -121,6 +125,16 @@ export type RateTrigger = typeof RATE_TRIGGERS[number];
 export const isCustomsClearanceTrigger = (trigger: string): boolean =>
   trigger === 'CUSTOMS_CLEARANCE' || trigger === 'ETHIOPIAN_CUSTOMS_CLEARANCE';
 
+/**
+ * The container hazardous-cargo surcharge: HAZARDOUS billed per container.
+ * It is sold per trade direction + origin → destination lane, optionally
+ * narrowed to one container type (20ft / 40ft), and priced by the
+ * route-matched block in RuleEngineService — never by the additive loop.
+ * The per-ton (bulk) hazard rate keeps the old global, unscoped shape.
+ */
+export const isContainerHazardRate = (trigger: string, rateUnit: string): boolean =>
+  trigger === 'HAZARDOUS' && rateUnit === 'PER_CONTAINER';
+
 @Entity({ schema: 'freight', name: 'rates' })
 @Index(['rateType'])
 @Index(['status'])
@@ -159,8 +173,10 @@ export class Rate extends BaseEntity {
   /**
    * The leg this rate prices. Base freight (trigger = ALWAYS) is quoted per
    * route — "container import, Djibouti → Dire Dawa" — so both yards are
-   * required for BULK/CONTAINER/INTERCITY and NULL for everything else. The
-   * `CK_rates_yard_scope` DB constraint enforces both halves of that.
+   * required for BULK/CONTAINER/EMPTY_CONTAINER/INTERCITY, for the lane-sold
+   * surcharges (customs clearance, empty return, fuel, container hazard) and
+   * NULL for everything else. The `CK_rates_yard_scope` DB constraint enforces
+   * both halves of that.
    */
   @Column({ name: 'origin_yard_id', type: 'uuid', nullable: true })
   originYardId?: string | null;