chore: bump version to 0.1.8 and update package name to @open-gitagen…

…t/gitagent

fix: --refresh now re-clones instead of git pull

git pull fails on shallow clones with divergent branches. Now --refresh
deletes the cached clone and does a fresh clone instead.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>