Creates a candidate on the specified position and returns the created candidate record.

• origin: sourced (the default) adds the candidate directly into the position's "Applied" stage, as if manually sourced. origin: applied instead runs the candidate through the same path as a public application: email_address is then required, the position must be published (otherwise 412), and if the position's application form has required fields not satisfied by the payload the API returns 202 and emails the candidate a link to complete them before the record is finalized (rather than 200 with the full candidate).
• Returns 409 if a candidate already exists on this position.
• stage_actions_enabled controls whether add-triggered stage actions fire for sourced candidates; they always fire when origin is applied.
• source, work_history, education, tags, social_profiles, and custom_attributes are validated and normalized (e.g. social profile keys must be from an allowed list, custom_attributes entries require name/value, and secure custom attributes get an _enc-suffixed id).