Apply changes to dataset items

Apply delta changes (add, edit, delete) to a dataset version with conflict detection. This endpoint: - Creates a new version with the applied changes - Validates that baseVersion matches the latest version (unless override=true) - Returns 409 Conflict if baseVersion is stale and override is not set Use `override=true` query parameter to force version creation even with stale baseVersion. Set 'copy_from_dataset_id' and 'copy_from_version_id' together on the request body to read carry-forward rows from the supplied (dataset, version) pair instead of the destination's prior version. When the fields are null, carry-forward rows are read from the destination's prior version.