comark/embed/missing-url · Give every ::embed a url

::embed reads its player or card from url alone, so a block without one renders nothing.

Incorrect

::embed{title="Vite in 100 Seconds"}
::

lint-comark example.mdexample.md:1:1 comark/embed/missing-url::embed 1: url is required.Write ::embed{url="https://..."}.✖ 1 problem

Correct

::embed{url="https://youtu.be/KCrXgy8qtjM" title="Vite in 100 Seconds"}
::

lint-comark example.md✔ No problems