fix: serve embed behavior as an enqueued script instead of inline markup

[erseco]

No translation changes: no strings change here, and since #148 code-only changes no longer touch the catalogs.

WordPress.org asked that plugins stop printing <script> and <style> blocks by hand and use the enqueue APIs instead. After this PR, plugin PHP prints none.

Frontend

• Block and shortcode: each printed an inline fullscreen/poster <script> per embed. One delegated script, assets/js/exelearning-embed.js, replaces both.
  • It is registered with exelearning-embed-loader in ExeLearning_Elp_Upload_Block::register_frontend_scripts(), hooked on init.
  • The block and the shortcode enqueue it by handle only when an embed renders.
  • No new class: the earlier ExeLearning_Embed_Assets wrapper was dropped.
• ExeLearning_Viewer_Enhancements: printed a <style> and a ResizeObserver <script> to turn a percentage height (for example height="75%") into pixels. CSS aspect-ratio produces the same box without script, and without the 150px collapse before the script ran. The class and its tests are removed, and the E2E height test is rewritten for aspect-ratio.

Standalone editor and export pages

These are full HTML documents written without a theme header, so there is no wp_head to print a queue into. They still use the queue, but print only their own handles:

• Scripts: each bridge is registered with wp_register_script() and enqueued with wp_enqueue_script(). Its configuration is added with wp_add_inline_script( …, 'before' ), which WordPress always prints before the src tag. Then wp_print_scripts( array( $handle ) ) prints that handle alone into an output buffer, with no theme or other plugin scripts.
• defer on the export bridge, kept on every supported version:
  • WordPress 6.3+ honours wp_script_add_data( $handle, 'strategy', 'defer' ).
  • For 6.1 and 6.2 a script_loader_tag filter adds the attribute. It is scoped to that handle and removed right after the print, and it only touches the first <script> tag with a src (the inline config arrives in the same string). A test simulates pre-6.3 core to cover it.
  • Passing array( 'strategy' => 'defer' ) to wp_register_script() is avoided on purpose: on 6.1/6.2 it is read as $in_footer = true.
• Styles: the editor page's CSS is registered and enqueued as an inline style (wp_register_style( false ) + wp_enqueue_style() + wp_add_inline_style()) and printed with wp_print_styles( handle ).

The embed scripts are registered on init, so the shortcode can enqueue them even where wp_enqueue_scripts never fires (the /embed/ template, previews).

Verification

• PHPUnit: all green, including new checks:
  • the config is printed inline before the bridge;
  • the export bridge is deferred and the editor's is not;
  • the bridge is printed exactly once;
  • the embed scripts are registered on init.
• npm run test:js: 258 passed, including every branch of exelearning-embed.js.
• WordPress Playground (the exact export page output):
  • 6.1.14: …-js-before config, then <script defer src=… id='exelearning-export-bridge-js'>;
  • 6.3.12: the same, with defer data-wp-strategy='defer'.
• make test-e2e for shortcode-viewer and viewer-enhancements: 38 passed.
• PHPCS clean with no NonEnqueuedScript exclusions left.

[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.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 98.85057% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 96.43%. Comparing base (8aed260) to head (c6f1ee7).

Files with missing lines	Patch %	Lines
includes/class-export-bootstrap.php	95.65%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #125      +/-   ##
============================================
+ Coverage     96.39%   96.43%   +0.04%     
+ Complexity      815      806       -9     
============================================
  Files            36       36              
  Lines          4213     4238      +25     
============================================
+ Hits           4061     4087      +26     
+ Misses          152      151       -1     

Flag	Coverage Δ
javascript	95.84% <100.00%> (+0.13%)	⬆️
php	96.64% <98.14%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
admin/views/editor-bootstrap.php	92.50% <100.00%> (+0.95%)	⬆️
assets/js/exelearning-embed.js	100.00% <100.00%> (ø)
exelearning.php	0.00% <ø> (ø)
includes/class-elp-upload-block.php	100.00% <100.00%> (ø)
public/class-shortcodes.php	100.00% <100.00%> (ø)
includes/class-export-bootstrap.php	90.72% <95.65%> (+0.72%)	⬆️

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