Ship default Header and Footer page_region configuration for Vartheme BS5 + Canvas

Problem/Motivation

Varbase Starter currently ships header and footer as block-layout regions. To give site builders a Canvas-first experience out of the box, the starter recipe should install header and footer as Canvas page regions wired to Vartheme BS5 SDC components.

Proposed resolution

#3584667: Add structured Header and Footer regions with Canvas page_region support

• Add default Canvas page_region configuration:
  • canvas.page_region.vartheme_bs5.header.yml
  • canvas.page_region.vartheme_bs5.footer.yml
• Update the canvas.component.sdc.vartheme_bs5.* config (page, page-footer, region, views, forms, taxonomy, user, etc.) to render header and footer content through SDC.
• Register the new config in recipes/varbase_starter/recipe.yml.

Remaining tasks

• ✅ 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
• ✅ Code review from 1 Varbase core team member
• ✅ Full testing and approval
• ✅ Credit contributors
• ✅ Review with the product owner
• ✅ Update Release Notes
• ❌ Release varbase-11.0.0-alpha1, varbase_starter-1.0.0-alpha1

User interface changes

• N/A

API changes

• N/A

Data model changes

• N/A

Release notes snippet

• feat: #3584668 Ship default Header and Footer page_region configuration for Vartheme BS5 + Canvas