Add support of AntiGravity Skills

[Extremys]

Hello,
It would be so great to add official support of AntiGravity installation of skills <3

There the details:

https://antigravity.google/docs/skills

~/.gemini/antigravity/skills// Global (all workspaces)

Thanks!

[BenjiMandel]

gemini-cli latest version also has skills now.