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]
```

Es wird keine Zieldokumentationsdatei und kein Test genannt. Beginne damit, den Dokumentationsbereich des Projekts zu finden, und überprüfe anschließend die Abschnitte zu Chromium, macOS und YubiKey sowie die darin verlinkten Downloads. Die Aufgabe ist abgeschlossen, wenn die Anleitung zur Schlüsselverwaltung am passenden Dokumentationsort platziert ist und die aufgeführten Anweisungen und Links korrekt sind.

Vom Indexierungsmodell aus dem Issue-Text verfasst.