apollo.listFields returns field IDs for customFields inputs and dynamic mappings.
automations/list-apollo-fields.automation.ts
source is "crm_synced" | "custom" | "system". Omitting it returns all sources. Optional second argument { account } selects the binding. Returns { fields } with fieldId, label, modality, type, contexts, source, metadata, workspace, and timestamps. Custom-field mutation inputs use fieldId as the key, not the label.