chore(deps): keep React aligned with WordPress

[erseco]

Summary

• pin react and react-dom to 18.3.1
• keep package-lock.json aligned with the manifest
• keep React dependency updates grouped
• ignore major React and React DOM updates in Dependabot

Why

The grouped React 19 update in #98 resolves the npm peer dependency conflict, but the JavaScript test suite then mixes React elements created by @wordpress/element@8.4.0 with react-dom@19. React 19 rejects elements created by the React 18 runtime shipped through the current WordPress packages.

The test environment also consumes @testing-library/react, which declares React and React DOM as peer dependencies. Keeping both packages explicit avoids relying on transitive dependency hoisting.

Impact

React remains aligned with the version used by the current WordPress package set. Dependabot can still group compatible updates, but it will not open automatic major-version updates until the WordPress dependencies are ready for React 19.

Validation

• parsed the updated .github/dependabot.yml
• verified the React group contains exactly react and react-dom
• verified both major-version ignore rules
• verified package.json and the root lockfile declarations use 18.3.1
• verified the lockfile resolves one root react@18.3.1 and react-dom@18.3.1

[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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.87%. Comparing base (75f51a9) to head (9cebef9).

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #100   +/-   ##
=========================================
  Coverage     96.87%   96.87%           
  Complexity      864      864           
=========================================
  Files            39       39           
  Lines          4323     4323           
=========================================
  Hits           4188     4188           
  Misses          135      135           

Flag	Coverage Δ
javascript	95.70% <ø> (ø)
php	97.25% <ø> (ø)

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