doc: How to Manage WebAuthn Keys: Browser, macOS, YubiKey, etc

## Chromium

- `chrome://settings/passkeys`
- `brave://settings/passkeys`

## macOS

- Search "passkeys" in macOS Settings

## YubiKey

- YubiKey Manager GUI (**deprecated**): \
To [install the pkg on macOS without allowing admin privileges](pkgutil --expand-full ~/Downloads/foo.pkg /tmp/foo/):
```sh
pkgutil --expand-full ~/Downloads/yubikey-manager-qt-1.2.5-mac.pkg /tmp/yubikey-gui/
mv "/tmp/yubikey-gui/com.yubico.ykman.pkg/Payload/YubiKey Manager.app" /Applications/
```
- YubiCo Authenicator: \
(haven't tried it yet, but might be able to do as much or more than the CLI)
- YubiKey Manager CLI:
```sh
pkgutil --expand-full ~/Downloads/yubikey-manager-5.5.0-mac.pkg /tmp/yubikey-cli
mv /tmp/yubikey-cli/ykman.pkg/Payload/usr/local/ ~/.local/opt/yubikey-v5.5.0
ln -s yubikey-v5.5.0 ~/.local/opt/yubikey
xattr -r -d com.apple.quarantine ~/.local/opt/yubikey/
ln -s ../opt/yubikey/bin/ykman ~/.local/bin/
```
and then make sure `~/.local/bin` is in your `PATH`, such as with (or `webi` itself).
```sh
pathman add ~/.local/opt/yubikey/bin/
```

The GUI doesn't seem to do much of anything. The CLI has more options:

```sh
# this definitely shows fewer accounts that I know I have, but I didn't find them under the other options either
ykman fido credentials list --csv
```

```csv
credential_id,rp_id,user_name,user_display_name,user_id
6ccd32400f0fc8cecfbaeca6932a53612477b57629ad1d36a461ca6e01342dd93df0af0f8db9d224d0f801482f22660e,local.pocketid.app,aj@therootcompany.com,aj,302e3430313230383733343534383933363335
```

```
ykman fido credentials delete [-f]
```

対象となるドキュメントファイルやテストは指定されていません。まずプロジェクトのドキュメント領域を見つけ、次に Chromium、macOS、YubiKey のセクションと、そこからリンクされているダウンロードを確認してください。キー管理に関するガイダンスが適切なドキュメントの場所に配置され、記載された手順とリンクが正確であれば完了です。

索引モデルが issue の本文から書いたものです。