Add a GitHub Actions workflow (package-extensions.yml) to build and upload Chrome/Firefox packages (store and offline artifacts) on manual trigger or when pushing v* tags. Update README with packaging instructions. Reorganize extension sources into chrome/ and firefox/ directories, add Firefox-specific files (manifest, locales, assets, CSS, LICENSE), and bump Chrome manifest version to 2026.04.23. Also modify js/oper.js (moved to chrome/js) to improve proportional editor resizing: add drag-to-resize, scale clamping/persistence (localStorage + chrome.storage.sync), pointer event handlers, and max-scale computation.
jonny