build: update Nextcloud webpack toolchain

[erseco]

Summary

• update @nextcloud/webpack-vue-config from 7.0.2 to 7.0.4
• update its required sass-loader peer from 16 to 17
• replace terser-webpack-plugin with minimizer-webpack-plugin
• require Node.js ^22.15.0 || ^24.0.0
• regenerate package-lock.json

Why

Dependabot PR #101 updated only @nextcloud/webpack-vue-config. Version 7.0.4 requires sass-loader ^17.0.0, while the app still declared sass-loader ^16.0.2, so every job that ran npm ci failed with ERESOLVE before frontend checks could start.

The updated toolchain also brings webpack-dev-server 6, whose minimum Node.js version is 22.15. This PR removes the no-longer-valid Node 20 claim while preserving the Node 22 line currently used by CI and Node 24 support.

This supersedes #101 with the complete, resolvable dependency update.

Impact

This affects development and asset compilation only. The Nextcloud app runtime does not require Node.js. Developers building assets now need Node.js 22.15+ on the Node 22 line, or Node.js 24.

Validation

• composer install
• npm install
• npm ci
• npm run typecheck
• npm run lint
• npm test — 108 tests passed
• make architecture-check
• make architecture-test
• npm run build
• vendor/bin/phpunit --configuration tests/phpunit.xml — 37 tests, 75 assertions
• make -n download-editor fetch-editor-source build-editor clean-editor build dev lint typecheck
• git diff --check

Local npm commands emitted expected EBADENGINE warnings because the local machine runs unsupported Node.js 26; dependency resolution, tests, and the production build completed successfully.

[github-actions]

Preview this PR in the Nextcloud Playground

A fresh Nextcloud boots in your browser with this branch's exelearning app installed and enabled (log in as admin / admin). Two sample .elpx are seeded under exelearning-samples/ in Files — click one to open the viewer.

eXeLearning editor: v4.0.3 (overlaid at boot from the upstream release).