ADM-OPERATION-551 - Get variants associated with an Operation

GET https://api.djust.example.com/admin/operations/{operationId}/lines

Returns the list of variants associated with a given Operation.

Feature flag
- Requires OPERATIONS to be active.

Access control
- OPERATOR clients can access any Operation.
- ACCOUNT clients can only access Operations they own (ownerId = customerUserId), and only if the OPERATIONS_READ permission is granted and they belong to the effective store (header dj-store if provided, otherwise tenant default store).

Filters
- Supported filters: variantIds, variantName, minQuantity, maxQuantity, recommendedQuantity.
- Filters are combined with logical AND. Multiple values of the same filter use OR logic.
- Unknown values are ignored.

Sorting
- Default sorting is by variantId|asc.
- Multiple sort criteria are supported among variantId, variantName, minQuantity, maxQuantity, and recommendedQuantity.