X / Twitter card generator

Generates the `twitter:` meta tags. Worth knowing you often do not need them at all — X falls back to your Open Graph tags when they are absent.

The one tag genuinely worth setting explicitly is `twitter:card`, because the default without it is the small summary card, which is far less prominent in the timeline than `summary_large_image`. Everything else — title, description, image — falls back to the Open Graph equivalents, so duplicating them is maintenance you can avoid and another place for the two to drift apart. The `twitter:image:alt` tag has no Open Graph equivalent and is worth adding for accessibility. Card validation moved behind a login some years ago, so the practical way to test is to post the link to a private account and look at it.