feat: add --version flag and self-update command

[abruption]

Add two CLI conveniences:

--version / -v

Print the installed version (currently only --help exists).

agy-cli-usage update

Self-update: check the registry for a newer version and run npm install -g agy-cli-usage@latest.

• update --check: report only, don't install.

Acceptance

• --version/-v prints version from package.json
• update checks latest vs current, installs if newer
• update --check reports without installing
• semver compare unit-tested
• CI green