Create person

Creates a Person record plus a citation on the same transaction.

**Required:** a profile body (at minimum `first_name` or `last_name`) and a citation with
`source_category` and an `http(s)` `url`.

**Body shapes accepted (pick one):**

1. Canonical nested — `{ "person": { … }, "source_reference": { … } }`.
2. Friendlier nested — same as above but `source` or `citation` instead of
`source_reference`; inside the citation, `category` is accepted for `source_category`.
3. Flat top-level — omit the `person:` wrapper and send profile fields at the top of the
body. Combine with `source: { … }` for the citation.

**Nested collections:** you may use Rails-style `name_aliases_attributes` /
`email_addresses_attributes`, or send the friendlier `aliases` / `emails` arrays. Arrays
can contain strings (`"Ada L"`, `"ada@example.com"`) or objects (`{ "name": "Ada L" }`,
`{ "address": "ada@example.com", "verified_at": "…" }`).

For the common "add a person (optionally under an organization)" case, prefer
`POST /api/v1/people/quick_add` — it takes a flat body and only requires
`first_name`, `last_name`, and `source_url`.

Requires an API key with `can_edit`. Costs one credit.