List pipeline fields

The field definitions of one pipeline. Entry values are keyed by each field's fieldId — read these to know which keys an entry accepts and how to render them (label, type).

Scoped by { project, targetSource: 'PIPELINE', pipeline } so it never leaks another pipeline's — or a session / company / ticket's — properties. The Frontend needs it to map the pipeline's columns (which store propertyId) onto entry.values (which is keyed by fieldId).