fix: switch to async spawn to unblock spinner animation and switch fr…

[whyuds]

Key Changes:
Async Spawn Implementation: Switched from synchronous child process execution to async spawn. This prevents the CLI from freezing and allows the loading spinner to animate correctly during repository cloning/installation.

Dependency Migration: Replaced ora with nanospinner. This provides a more lightweight spinner implementation.

Warning Fix: Resolved the (node:32292) ExperimentalWarning: Importing JSON modules warning that appeared in newer Node.js versions.

PS D:\git\github\whyuds\openskills> openskills install git@github.com:whyuds/skills.git
(node:32292) ExperimentalWarning: Importing JSON modules is an experimental feature and might change at any time
(Use `node --trace-warnings ...` to show where the warning was created)
Installing from: git@github.com:whyuds/skills.git
Location: project (.claude/skills)

⠋ Cloning repository...