Add a site-wide switch to disable embedded editing (DEC-0066)

[erseco]

What

A new admin setting, Disable the embedded editor (exelearning/editordisabled, unticked by default), lets a site use the plugin as a pure .elpx player: uploading and serving packages keeps working exactly as before, but the "Edit with eXeLearning" button is hidden and the editor endpoints refuse requests.

Why a negative checkbox

The first iteration used a positive "Enable the embedded editor" with default Yes — and rendered unticked next to "Default: Yes" on any site where upgradesettings had not yet materialised the default, contradicting the real behaviour. With the negative toggle, the unset config and the unticked box always mean the same thing: editing on. Same pattern as the plugin's existing stylesblockimport setting. The default behaviour is unchanged: the editor stays enabled unless an administrator ticks the box.

Why a setting and not a capability

Recorded in ADR DEC-0066 (included in this PR). The who of editing is already governed by moodle/course:manageactivities, consistent with the rest of the plugin; the real use case is binary and site-wide ("this site does not edit in place"), which is what activity plugins normally express as a feature switch in admin settings. A per-role capability would force sites to edit role definitions for a yes/no decision — and can still be added on top later without breaking anything, with the setting remaining the master switch.

How

• exelearning_embedded_editor_enabled() now combines the toggle with bundle validation (DEC-0065), so everything that already consulted it reacts at once: the edit button in view.php, the asset router editor/static.php, and the create-from-scratch CTA (which degrades to the "upload a package" hint).
• Hiding a button is not an access control, so direct requests are refused too: editor/index.php shows an explanatory error page and editor/save.php — the state-changing half — aborts through the new exelearning_require_embedded_editor_enabled() guard.
• Strings added to the five language packs (machine translations carry the ~ review marker, per repo convention); README, docs/EMBEDDED_EDITOR.md and the user guide document the switch.

Tests

Written first and watched failing: with a valid bundle and the toggle ticked, the helper reports false and the endpoint guard throws moodle_exception; with no config at all, editing stays on and the guard passes. Suite: 7/7 locally on the helper file (Moodle 5.0.7 / PHP 8.3 / MariaDB), phpcs --standard=moodle 0/0 on every touched file.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.31%. Comparing base (f39f7e7) to head (7c4a140).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #108   +/-   ##
=========================================
  Coverage     92.30%   92.31%           
  Complexity      824      824           
=========================================
  Files            51       51           
  Lines          3730     3734    +4     
=========================================
+ Hits           3443     3447    +4     
  Misses          287      287           

Flag	Coverage Δ
javascript	94.11% <ø> (ø)
php	92.23% <100.00%> (+<0.01%)	⬆️

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

Components	Coverage Δ
PHP (server-side)	92.23% <100.00%> (+<0.01%)	⬆️
JavaScript (SCORM tracker)	94.11% <ø> (ø)

Files with missing lines	Coverage Δ
lib.php	80.13% <100.00%> (+0.27%)	⬆️

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.