[BUG] pi is incorrectly marked as not supporting skills

[llimllib]

Describe the bug

#560 gave a better error message when attempting to install a skill to a platform that does not support them, but it incorrectly asserts that pi is one of those platforms

documentation: https://pi.dev/docs/latest/skills

pi supports skills, and its default path is ~/.pi/agent/skills. It also supports ~/.agents/skills by default; I'm not sure what other platforms do.

To Reproduce

Steps to reproduce the behavior:

1. pup skills install --name dd-apm pi
2. get an incorrect error message: Error: no install target matched name=dd-apm on the selected platform(s): pi. pi only support extensions, not skills or agents. Available extension(s): dd-pup-pi

Expected behavior

pup installs the skill to pi, which supports skills

Environment

• OS: mac
• Pup version: 0.65.2
• Authentication method: OAuth2

Command output

$ pup skills install --name dd-apm pi
🔄 Access token refreshed automatically.
Error: no install target matched name=dd-apm on the selected platform(s): pi. pi only support extensions, not skills or agents. Available extension(s): dd-pup-pi