feat(canopy-applications): authorized representative endpoints

Source: application-intake plan Potential Improvements.

applications.authorized_representative_id is on the schema but no CRUD endpoints exist. ACA §1413 requires support for authorised representatives filing on behalf of applicants.

Acceptance: POST/GET/DELETE /v1/authorized-representatives to manage representative records; POST /v1/applications accepts authorized_representative_id; representative listing scoped to a person or household.