ADM-OPERATION-350 - Remove variants from an Operation

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

Removes one or more variants from a specific Operation.

Feature flag
- Requires OPERATIONS to be active.

Access control
- OPERATOR: can remove variants from any Operation (no store constraint).
- ACCOUNT: can remove variants only from Operations they own (ownerId = customerUserId) and if they have the OPERATIONS_UPDATE right.

Store scoping
- Effective store is the dj-store header if provided, otherwise the tenant default store.
- ACCOUNT must be attached to the effective store; otherwise 403.

Constraints
- Only Operations in DRAFT status accept line removals.
- Request body must be a non-empty array of external variant identifiers (strings).
- Unknown variantId values are ignored; processing continues.
- If none of the provided variantId values are valid for the Operation, the API returns 404.