fix: guard husky prepare script for non-dev installs

[dstude]

Problem

When users install sidecar globally via:

npm install -g https://github.com/jrenaldi79/sidecar

npm runs the prepare script as part of installation. Since husky is a devDependency, it isn't present in a global install context — causing the install to fail immediately with a missing module error, before sidecar is usable at all.

Fix

Guard the prepare script so husky only runs when inside a git checkout:

"prepare": "[ -d .git ] && husky || true"

This means:

• Dev installs (cloned repo): husky installs normally
• Global installs (no .git dir): the script exits cleanly

This is the standard pattern recommended for projects that support both development and end-user installs. No behavior change for contributors.

[jrenaldi79]

Recreated as same-repo PR #28 to enable CI workflows (fork PRs don't get secret access). See #28.