Twitter Card Image URL Malformed

Current template for the `twitter:image` meta tag incorrectly prepends `http://schoolido.lu` ahead of the actual path to the image (e.g. an AWS url)

See:
[web/templates/base.html, line 24](https://github.com/SchoolIdolTomodachi/SchoolIdolAPI/blob/d19ca35ace1aca3316c9c68c7edbd4b7ae67d5d2/web/templates/base.html#L24):

```

```

      +
[web/templates/cards.html, line 14](https://github.com/SchoolIdolTomodachi/SchoolIdolAPI/blob/d19ca35ace1aca3316c9c68c7edbd4b7ae67d5d2/web/templates/cards.html#L14):

```
{% block shareimagetwitter %}{% if single %}http://schoolido.lu{{ single|imageurl:'card_idolized_image' }}{% else %}http://schoolido.lu/static/cards_screenshot.png{% endif %}{% endblock %}
```

will yield

```

```

(as an example)

Start with web/templates/base.html at line 24 and web/templates/cards.html at line 14, then trace the imageurl output used for card images. Render both the default and single-card cases and verify that twitter:image contains a valid absolute URL without a duplicated host prefix.

Written by the indexing model from the issue text.