test: enhance npm pack tests with comprehensive installed package tests

Extend test/pack.test.ts to include comprehensive tests for the
installed npm package, ensuring that the package created by npm pack
(which runs prepack and is closest to the final release) works
correctly after installation.

The enhanced test suite includes:
- Command tests: verify all CLI commands (install, exec,
  check-update, --help) work in installed package
- Functionality tests: verify core features (Change-Id generation,
  Co-developed-by generation for all AI tools, priority ordering)
  work correctly in installed package
- Module import tests: verify modules can be imported and
  configurations loaded from installed package
- Git integration tests: verify complete workflow in real Git
  repository using installed package

This ensures that the packaged software (closest to what users
install) works correctly in all scenarios, catching any issues
that might only appear after npm install but not in development
or dist/ build tests.

Change-Id: Ic7ff635d9ef2eb1d583ee24b5b381dbfa82104c4
Co-developed-by: Cursor <noreply@cursor.com>

Author: jiangxin