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.