Set the `card` class directly on the `post-linkarea`

Can we set the `card` class on the `post-linkarea` to save on markup? (just an idea, it can be done is another ticket)
```suggestion
<post-linkarea class="card">
```

_Originally posted by @alizedebray in https://github.com/swisspost/design-system/pull/5966#discussion_r2304008978_


Examples in both the `post-linkarea` and `card` component would need to be changed.

            