refactor: #3609251 Convert hooks to the Drupal 11 OOP hook system and validate on Drupal ~11.4

Closes #3609251.

Converts the module's hooks to the Drupal 11 OOP hook system and validates the CI on the real Drupal ~11.4 target.

• Moves hook_page_attachments, hook_theme, hook_theme_registry_alter and hook_preprocess_varbase_dashboards_admin_list (plus the back-end layout helper functions) into src/Hook/VarbaseDashboardsHooks.php with constructor dependency injection (registered autowire: true in varbase_dashboards.services.yml); deletes the procedural varbase_dashboards.module. Behaviour is preserved.
• Pins the CI composer job to DRUPAL_CORE: "11.4.0" (+ IGNORE_PROJECT_DRUPAL_CORE_VERSION) so the pipeline actually builds and runs the webship-js suite on Drupal ~11.4 instead of the DrupalCI template default.

AI-Generated: Yes (Used Claude Code to convert the hooks to OOP with DI and pin the CI to Drupal 11.4), reviewed and authorized by the maintainer, per the AI contribution policy.

Checkpoints

• File an issue about this project
• Addition/Change/Update/Fix to this project
• Testing to ensure no regression
• Automated unit/functional testing coverage
• Developer Documentation support on feature change/addition
• User Guide Documentation support on feature change/addition
• UX/UI designer responsibilities
• Accessibility and Readability
• Reviewed by a human
• Code review by maintainers
• Full testing and approval
• Credit contributors
• Review with the product owner
• Update Release Notes
• Release