add per-container handling options for hazardous, reefer, and return services

- Introduced new boolean fields (isHazardous, isReefer, isReturn) in UnitDraft and related interfaces to allow individual container handling options.
- Updated emptyUnit function to initialize these new fields.
- Modified GlCreateBookingForm to handle and display these options for each container.
- Adjusted calculations for hazardous, reefer, and return quantities based on the new handling options.
- Updated the schema for container units and booking container lines to include handling options.
- Added migration to support the new return flag in the database.
- Enhanced various components to reflect gross weight calculations, ensuring consistency across the application.

packages/types/src/freight/contracts.ts

@@ -729,14 +729,22 @@ export interface CreateContainerUnitDto {
   containerNumber: string;
   sealNumber?: string;
   vgmTons: number;
+  /** Per-container handling opt-ins, entered alongside this container's VGM. */
   isHazardous?: boolean;
   isReefer?: boolean;
+  /** This container ships back empty (equipment return). */
+  isReturn?: boolean;
 }
 
 export interface CreateBookingContainerLineDto {
   /** "20ft" | "40ft" — must be in the contract's cargo scope. */
   containerSize: string;
   quantity: number;
+  /**
+   * Line totals, derived from the per-unit switches above. The API recomputes
+   * them from `units` whenever any unit carries a flag, so they are only
+   * authoritative for callers that don't send per-unit flags.
+   */
   hazardousQuantity?: number;
   reeferQuantity?: number;
   /**