feat: #3615236 Add the header search box to the Varbase Starter header region

Issue: https://www.drupal.org/project/varbase_starter/issues/3615236

What/why

Places the Icon Toggle (Inline bar panel style) at the end of the header group after the main menu, with the "Exposed form: search-page" block in its content slot, and adds the two new component config dependencies.

Ships the two component configs the region depends on. Both were exported from a working site and normalised to the active version only, matching the shipped "Exposed form: blog-all" component config.

Adds a recipe config action that sets the search view's exposed placeholder to "Search by keyword", so the wording is not changed by patching the third-party Drupal CMS Search recipe.

Depends on Vartheme BS5 issue #3593698 being merged and released first — the stored component version hash in config/canvas.component.sdc.vartheme_bs5.icon-toggle.yml comes from the new bar panel prop added there. This recipe change has not yet been verified by a fresh site install (it applies at recipe-apply time); local checks were config/YAML validation only.

AI-Generated: Yes

Checkpoints:

• 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
• Developer Documentation
• User Guide Documentation
• Reviewed by human
• Code review by maintainers
• Full testing and approval
• Credit contributors
• Review with the product owner
• Release notes snippet
• Release