- removed dependency on `jupyterlab 3`
- **note**: this doesn't mean it will "just work" with JupyterLab 4
- add basic syntax highlighting with `deathbeds/codemirror-pikchr`
- vendor `pikchr.wasm` from fossil 2.20
- widget
- rename `dark` to `dark_mode`
- add `css_class`
- document
- add toolbar with buttons for `fit` and `tag`
- mime
- fallback `text/html` outputs get populated after rendering in the browser
- metadata
- rename `dark` to `darkMode`
- add `cssClass`