Fix CLI version output

[MrDiscipline]

Fixes #1.

Summary

• read the CLI version from package.json instead of a stale hardcoded string
• add a regression test that runs the CLI --version path and compares it to the package version

Verification

• npx -y bun@latest test test/cli.test.ts
• npx -y bun@latest test test/
• npx -y bun@latest run build
• npm pack, clean install the tarball, then verify:
  • webtool --version prints 0.3.3
  • agent-webtool --version prints 0.3.3