Surface newsletter state on /api/auth/me (or self GET /api/people/:slug)

Follow-up from [#38](https://github.com/CodeForPhilly/codeforphilly-ng/pull/38) (authoring-screens).

The Account settings screen has a working newsletter toggle that PATCHes `/api/people/:slug/newsletter`, but the read side never exposes the current opt-in state to the SPA. `GET /api/auth/me` returns the public Person shape (no newsletter); the people serializer hides newsletter from non-self callers.

Result: the Account screen defaults to `optedIn=false` and only reflects the server state after the user toggles once. That's a UX bug — a user who opted-in on a previous session sees a checkbox that lies until they touch it.

### Fix

Add `newsletter.optedIn` (and probably `email`) to the self-view of `GET /api/auth/me` (and/or `GET /api/people/:slug` for self). The `PATCH /api/people/:slug/newsletter` response already returns the full `newsletter` shape, so the data is available — the serializer just needs to include it for self.

### References

- [specs/screens/account.md](../specs/screens/account.md) — Newsletter card spec
- [specs/api/auth.md#get-apiauthme](../specs/api/auth.md) — "The PersonResponse for self includes `email` (fetched from PrivateProfile) and `newsletter` state." (already in the spec; just unimplemented)

Bắt đầu với specs/api/auth.md#get-apiauthme và specs/screens/account.md, sau đó truy vết serializer được GET /api/auth/me và self view của GET /api/people/:slug sử dụng. Thay đổi hoàn tất khi self response bao gồm newsletter.optedIn và email, khớp với PersonResponse được ghi trong tài liệu và cấu trúc response của newsletter PATCH.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.