Add GitHub Actions CI + RubyGems release pipeline with pre-build version gate

[Copilot]

This PR adds GitHub Actions workflows for deployment/release automation and RubyGems publishing. It also enforces a release safety check so publishing only proceeds when the gem version has been bumped above the latest version already published on RubyGems.

• CI workflow (.github/workflows/ci.yml)

  • Runs on push and pull_request
  • Executes test + gem build on Ruby 3.2, 3.3, 3.4
  • Sets minimal workflow permissions (contents: read)

• Release workflow (.github/workflows/release.yml)

  • Triggers on release.published and workflow_dispatch
  • Splits into verify and publish jobs
  • Publishes to RubyGems via rubygems/release-gem@v1 using RUBYGEMS_AUTH_TOKEN
  • Uses minimal permissions and a dedicated rubygems environment

• Version bump enforcement before build

  • In verify, compares local CloudstackClient::VERSION against RubyGems latest (cloudstack_client)
  • Fails early if local version is not greater, preventing accidental duplicate/invalid releases

- name: Ensure version is bumped
  run: |
    CURRENT_VERSION="$(ruby -Ilib -e "require 'cloudstack_client/version'; puts CloudstackClient::VERSION")"
    LATEST_JSON="$(curl -fsSL https://rubygems.org/api/v1/versions/cloudstack_client/latest.json || true)"
    if [ -n "$LATEST_JSON" ]; then
      LATEST_VERSION="$(printf '%s' "$LATEST_JSON" | ruby -rjson -e "puts JSON.parse(STDIN.read)['version']")"
      ruby -e "require 'rubygems/version'; current = Gem::Version.new('$CURRENT_VERSION'); latest = Gem::Version.new('$LATEST_VERSION'); abort('Version must be bumped before building') unless current > latest"
    fi

• Documentation update (README.md)
  • Adds GitHub Actions release/CI notes
  • Documents required secret: RUBYGEMS_AUTH_TOKEN
  • Notes version bump check behavior