Add automated version checking for AltumCode products and plugins:
- isAltumPlatform() routes altum vendors before OSS checks
- checkAltumProduct() fetches latest_release_version from product info.php
- checkAltumPlugin() looks up plugin versions from dev.altumcode.com
- In-memory cache avoids redundant HTTP calls for multiple plugins
14 Pest tests covering all paths (43 assertions).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
