Add CI, apply drupal-extension-scaffold, and fix code style - #8

…alCI

Applies the drupal_extension_scaffold (v4.17.0) for standardized local
development and CI tooling, on top of Julian Pustkuchen's .gitlab-ci.yml
and Kieran Cott's DI refactor (MR !13), then makes the full pipeline
(phpcs, phpstan, rector, eslint, cspell, phpunit) actually pass:

- Remove legacy .circleci/ setup, replaced by .gitlab-ci.yml + .github/
- Resolve all PHPStan errors and add strict_types across the module
- Fix D10/D11 cross-version PHPStan/Rector conflicts (drupalCreateUser()
  return-type narrowing needed on D10 but redundant on D11; skip the two
  Rector rules that would convert PHPUnit annotations to attributes,
  which D10's PHPUnit 10 doesn't support)
- Remove DrevOps/PHPCompatibility/testVersion from phpcs.xml and exclude
  rector.php from phpstan.neon - sniffs/classes not available in
  DrupalCI's environment
- Drop the phpstan.neon ignoreErrors path restriction that never matched
  DrupalCI's checkout-root scan context (paths report without the
  web/modules/custom/ prefix there, unlike the local build/ tree)
- Exclude .devtools/ from phpcs (scaffold infrastructure, not module code)
- Drop .eslintrc.json's airbnb-base extend and .prettierrc.json's
  @homer0/prettier-plugin-jsdoc plugin - both fail to resolve under
  DrupalCI's core-only node_modules; keep yml/prettier plugin support
  since DrupalCI also lints this module's own YAML files
- Configure DrupalCI GitLab CI variables and add phpunit.gitlab-ci.xml
- Add cloudflared dev-tunnel scripts, wire DRUSH_URI into drush/login,
  and wire the missing start-/stop- hook calls into .devtools/start and
  .devtools/stop so the tunnel scripts actually run (the scaffold's
  .devtools/provision already called its provision- hook; start/stop
  never called theirs)

Confirmed all gitlab.local pipeline jobs pass (phpcs, phpstan, eslint,
phpunit, cspell, composer-lint) on both Drupal 10 and Drupal 11.