services module: confirm default values for ApiPerson v4 invitationStatus/linkedAccounts

## Context

In `packages/modules/services/src/people/api-models.v4.ts`, two fields on the v4 `ApiPerson` model are marked with an open question about their default value:

```ts
// TODO is this default
invitationStatus?: ApiInvitationStatus;
accountClassification?: ApiAccountClassification;
managerAzureUniqueId?: string;

// TODO is this default
linkedAccounts?: Array;
```

## Task

- Confirm with the People API v4 contract/docs (or API owners) what default value(s), if any, `invitationStatus` and `linkedAccounts` have when omitted from a response.
- Update the type/comments to document the confirmed default behavior, or mark the fields as required if the API always returns them.

## File

`packages/modules/services/src/people/api-models.v4.ts` (lines ~53, ~58)

Start in packages/modules/services/src/people/api-models.v4.ts around lines 53 and 58, then check the People API v4 contract or consult the API owners about omitted invitationStatus and linkedAccounts values. Done means the confirmed defaults are documented in the comments or types, or the fields are marked required if the API always returns them.

Written by the indexing model from the issue text.