Add the header search box to the Varbase Starter header region

Problem/Motivation

Varbase Starter ships the global Header region with site branding and the main menu only. A fresh Varbase Starter site therefore has no way to search from the header, even though the site template already installs the search view (views.view.search, path /search) through Drupal CMS Search. The approved Varbase header design has a search icon at the end of the header that opens a search bar.

Steps to reproduce

1. Install Varbase 11 with the Varbase Starter site template.
2. Look at the header on any page.

Result: no search control anywhere in the header.

Proposed resolution

• In config/canvas.page_region.vartheme_bs5.header.yml, place the Icon Toggle (with the new "Inline bar" panel style) at the end of the header group, after the main menu, and put the "Exposed form: search-page" block in its content slot. Add both new config dependencies.
• Ship the two component configs the region now depends on: config/canvas.component.sdc.vartheme_bs5.icon-toggle.yml and config/canvas.component.block.views_exposed_filter_block.search-page.yml.
• In recipe.yml, add a config action setting the search view's exposed placeholder to the design's wording ("Search by keyword") instead of Drupal CMS Search's default "Enter search keywords". Doing it as a recipe action avoids patching the third-party Drupal CMS Search recipe.

Depends on the Vartheme BS5 issue "Style the Search in the Header" (#3593698) — the Icon Toggle "Inline bar" panel style — being merged and released first, because the stored component version hash comes from the new component definition.

AI-Generated: Yes

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
• ➖ 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 varbase_starter-1.0.0-rc1

User interface changes

• The header gains a search icon that opens a search bar; the search field placeholder reads "Search by keyword".

API changes

• No.

Data model changes

• No. Config only (one updated page region, two new component configs, one recipe config action).

Release notes snippet

• The Varbase Starter header now ships a search box: a search icon at the end of the header opens a search bar wired to the site search page.