test: cover editor controller orchestration

[erseco]

Summary

• extract pure editor HTML injection into EditorHtmlService
• cover base/config injection, resilience shim, and save bridge in a pure service test
• cover EditorController authentication, id/path resolution, initial state, CSP, save error paths, missing editor, and iframe response
• add EditorController to the backend Clover scope
• keep the 90% backend threshold

Stack

Depends on #122 → #121 → #120 → #119.

This is the final planned PR in the stacked PHP coverage series.

Validation

• CI: green
• Playground preview: green
• backend line coverage: 92.42%
• Codecov processed tree:
  • lib/: 93.03%
  • lib/Controller: 92.78%
  • lib/Service: 95.92%
  • lib/AppInfo: 100%
  • lib/Preview: 83.33%
  • src/: 95.45%
• EditorController: 85% lines
• EditorHtmlService: 100% lines
• LegacyFileMigrationService: 100% lines

[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: v4.0.5 (overlaid at boot from the upstream release).

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (refactor/editor-legacy-migration-service@6422b8b). Learn more about missing BASE report.

Additional details and impacted files

@@                             Coverage Diff                             @@
##             refactor/editor-legacy-migration-service     #123   +/-   ##
===========================================================================
  Coverage                                            ?   93.75%           
  Complexity                                          ?      150           
===========================================================================
  Files                                               ?       22           
  Lines                                               ?      657           
  Branches                                            ?       54           
===========================================================================
  Hits                                                ?      616           
  Misses                                              ?       34           
  Partials                                            ?        7           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.