Fix bootstrap test failures in CI by installing uv package manager.
The bootstrap script (scripts/bootstrap_skill.sh) requires uv to run,
which was causing 7 bootstrap E2E tests to fail in CI with:
'uv: command not found'
Changes:
- Install uv via official installer (works on Ubuntu & macOS)
- Add uv to PATH for subsequent steps
This resolves the failing tests from PR #251 merge.
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>