Add XML documentation for Android.App.People

The `Android.App.People` namespace contains **110** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

Example command:

```powershell
rg -n -i --glob 'Android.App.People/**' --glob 'ns-Android.App.People.xml' 'to be added' docs\xml
```

## Update log

- 2026-09-10: Refreshed the placeholder scan from **108** to **110** (increased by **2**). Related documentation PRs: [#644](https://github.com/dotnet/android-api-docs/pull/644).

Start with the Android.App.People/** and ns-Android.App.People.xml files under docs\xml, using the provided rg command to locate the 110 "To be added" placeholders. Replace the placeholders with XML documentation and rerun the scan; done means no matching placeholders remain in this namespace, excluding docs\xml\index.xml.

索引モデルが issue の本文から書いたものです。