feat: implement 20ft container weight-pairing validation

- Added ContainerValidationService to handle 20ft weight-pairing logic.
- Introduced validate20ftWeightPairing utility function to check weight differences.
- Updated BookingPricingService to include overweight line details and pairing errors in price response.
- Enhanced BookingTransitionService to reject submissions with unpairable 20ft containers.
- Created ShipmentValidation interface for pre-submit validation of container contracts.
- Integrated shipment validation into the contract booking process, providing warnings for overweight containers and hard blocks for pairing errors.
- Updated front-end components to display validation results and prevent submission when errors are present.

apps/edr-freight-api/src/modules/contracts/contracts.controller.ts

@@ -788,6 +788,18 @@ export class ContractsController {
     );
   }
 
+  @Post(':id/validate-shipment')
+  @ApiOperation({
+    summary:
+      'Pre-create validation: overweight lines + 20ft weight-pairing errors for a shipment payload (no booking created).',
+  })
+  validateShipment(
+    @Param('id', ParseUUIDPipe) id: string,
+    @Body() dto: CreateBookingUnderContractDto,
+  ) {
+    return this.contractBookingService.validateShipment(id, dto);
+  }
+
   @Get(':id/capacity')
   @ApiOperation({
     summary: 'Remaining bookable quantity per cargo line (GENERAL draw-down cap)',