Add automated functional acceptance testing for Ace Editor with webship-js (Playwright + Cucumber-js), GitLab CI, and MkDocs documentation

Problem/Motivation

Ace Editor has no automated functional (browser) test coverage, no end-user documentation and no self-contained CI pipeline.
Without acceptance tests, regressions in the three ways the module surfaces the Ace editor — the text editor on forms,
the Ace Format field formatter, and the Ace Filter for <ace> snippets — go unnoticed. While
building this coverage on Drupal 11, several functional and coding-standard defects were also found.

Defects found while writing the tests

• Permission never registered — the file was named ace_editor.permission.yml (singular). Drupal
  only loads <module>.permissions.yml, so administer ace_editor was never registered.
• Print margin never shown — js/editor.js, js/formatter.js and
  js/filter.js read a non-existent print_margin key, while the config/UI key is
  print_margins.
• Filter / formatter behaviour collision — js/filter.js registered
  Drupal.behaviors.ace_formatter (the formatter's name), so on a page rendering both, one clobbered the other. The
  per-<ace>-tag attribute overrides were also computed but never applied.
• Label typo — the "Enable Autocomplete (Ctrl+Space" checkbox label was missing its closing parenthesis.

Proposed resolution

Automated functional acceptance testing (webship-js)

• Add a webship-js (Playwright + Cucumber-js) BDD suite under
  tests/features/drupal/** — 12 scenarios / 76 steps covering: the text editor attaching and syncing to the textarea,
  the print-margin regression, the editor settings form, the read-only field formatter, the <ace> filter, per-tag
  attribute overrides, and accessibility (axe).
• Custom step definitions, named selectors, shared world parameters and a tests/fixtures/provision-fixtures.php
  that configures the editor/filter/formatter and demo content through Drush.

GitLab CI

• .gitlab-ci.yml — the drupalci validation gates (composer-lint, cspell, eslint, phpcs, phpstan, phpunit) plus a
  webship-js-test job that installs a Drupal Standard site, downloads the Ace library, provisions fixtures and runs the
  suite.
• .gitlab-ci-local.yml — a self-contained pipeline for href="https://github.com/firecow/gitlab-ci-local">gitlab-ci-local (cspell, eslint, MkDocs --strict, and a full
  webship-js-test that builds a fresh Drupal 11 site via a Composer path repository). All jobs validated green
  locally.

Documentation (MkDocs)

• Add Material-for-MkDocs documentation under docs/ + mkdocs.yml: introduction, installation, using
  the editor/formatter/filter, configuration, themes & syntaxes, permissions, architecture and library detection, plus an
  FAQ.
• Add a README.md to every module folder.

Bug & coding-standard fixes

• Rename ace_editor.permission.yml → ace_editor.permissions.yml.
• Honour print_margins in all three behaviours, still accepting the legacy print-margin inline
  attribute.
• Register the filter as Drupal.behaviors.ace_filter and apply per-tag overrides without mutating shared
  defaults.
• Fix the autocomplete label and resolve phpcs (Drupal/DrupalPractice) issues.

Remaining tasks

• ✅ File an issue
• ➖ Addition/Change/Update/Fix
• ➖ Testing to ensure no regression
• ➖ Automated unit testing coverage
• ➖ Automated functional testing coverage
• ➖ UX/UI designer responsibilities
• ➖ Readability
• ➖ Accessibility
• ➖ Performance
• ➖ Security
• ➖ Documentation
• ➖ Code review by maintainers
• ➖ Full testing and approval
• ➖ Credit contributors
• ➖ Review with the product owner
• ➖ Release notes snippet
• ❌ Release

API changes

• N/A

Data model changes

• N/A

Release notes snippet

• N/A