feat: #3610873 Initialize Varbase Events Base recipe

Initial import of drupal/varbase_events_base.

Issue: https://www.drupal.org/project/varbase_events_base/issues/3610873

Adds an Event content type and an events listing on top of the contrib Events recipe (drupal/events), wired the Varbase way (sub-recipes varbase_content_base, varbase_media_base, varbase_seo_base, varbase_workflow_base, events; selective_better_exposed_filters, webshare). Includes the /events listing (Canvas grid, filters, "Related events" block) and Drupal Canvas content/card templates.

Must be applied after varbase_starter in a site template — Canvas only generates a theme's components on RecipeAppliedEvent. The event content template ships as a config action (not a config file) because core pre-creates the empty display alongside the bundle.

Verified: installs clean (0 errors) on varbase_starter + varbase_events_base; /events and an event page return HTTP 200.

AI-Generated: Yes (Used Claude Code to build the recipe and verify the install).

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