feat(playground): auto-load the editor in the WordPress Playground

[erseco]

What

Auto-load the embedded eXeLearning editor in the WordPress Playground so it boots with a working editor instead of requiring the manual Settings → eXeLearning → Download & Install Editor button.

Two blueprint steps after installPlugin:

1. writeFile fetches the shared editor release asset through the github-proxy (CORS) over the fast JS transport into /tmp/exe-editor.zip.
2. runPHP locates the installed plugin dir and extracts the zip into its dist/:

$dirs = glob(WP_PLUGIN_DIR . '/wp-exelearning*', GLOB_ONLYDIR);
$zip = new ZipArchive;
$zip->open('/tmp/exe-editor.zip');
$zip->extractTo($dirs[0] . '/dist');   // asset wraps in static/ -> dist/static/

Why

The static editor is byte-identical across all eXeLearning plugins and is already published once at exelearning/exelearning. Fetching that shared artifact at blueprint time is the WordPress-Playground-idiomatic pattern (resource url + extract), and it keeps the plugin zip lean.

Notes:

• The plugin is installed from the branch source archive, so its directory carries a branch suffix (wp-exelearning-<branch>); the extract step finds it with a glob, so it works on any PR.
• ZipArchive is already used by the fixtures step, so no new runtime dependency.
• The asset's static/ wrapper means extracting into dist yields the dist/static/ layout the plugin loads from (EXELEARNING_PLUGIN_DIR . 'dist/static/index.html'). Pinned to v4.0.0 to match .editor-version.
• StaticEditorInstaller is kept for production/offline installs; only the playground changes.

Part of a fleet-wide change unifying how the editor loads in every eXeLearning playground.

Test

Open the Playground for this branch and confirm the editor loads on boot (no manual step) and a page renders.

[github-actions]

Test in WordPress Playground

Test the plugin with the code from this branch:

ℹ️ The eXeLearning editor is fetched from the shared release and unpacked into the plugin when the playground boots, so the first load may take a few extra seconds. ELP upload, shortcode, Gutenberg block and preview work normally.