[FEATURE] Skills install syntax support having compatibility with that of Vercel

[lirantal]

Is your feature request related to a problem? Please describe.
Support skill install syntax similar to that of Vercel skills npx package

Describe the solution you'd like
Example:

npx skills add https://github.com/anthropics/skills --skill frontend-design

As you can see, it uses a --skill flag, unlike currently in apm which requires a full directory part in the git repo. It also accepts the github URL syntax (https://github.com/) instead of only owner/repo format.

Describe alternatives you've considered
It would be a nice DX to be able to swap between Vercel skills and that of apm easily.