Browser installer lands on // because the site template finish_url has a leading slash

Problem/Motivation

The site template declares its post-install redirect with a leading slash in recipe.yml:

extra:
  finish_url: /admin/dashboard/welcome

Core's install_goto() prepends the base path, so the leading slash is doubled and the browser installer sends the user to https://example.com//admin/dashboard/welcome.

This recipe value, not the profile's, is the one that fires: Varbase's SiteTemplateForm::submitForm() copies the site template's extra.finish_url into $install_state['parameters']['finish_url'], so the installer URL carries finish_url=/admin/dashboard/welcome.

drupal_cms_installer declares the same value without a leading slash, which is the convention to match.

Steps to reproduce

1. Build a Varbase 11 project with the Educare site template available in recipes/.
2. Go to /core/install.php and pick Educare.
3. Complete the installer.
4. The browser lands on //admin/dashboard/welcome instead of /admin/dashboard/welcome.

Proposed resolution

Drop the leading slash:

extra:
  finish_url: 'admin/dashboard/welcome'

Verified on a browser install: the installer URL then carries finish_url=admin/dashboard/welcome and the site lands on the correct path with no doubled slash.

Remaining tasks

• ✅ File an issue
• ❌ Addition/Change/Update/Fix
• ❌ Testing to ensure no regression
• ➖ Automated unit testing coverage
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• ➖ UX/UI designer responsibilities
• ➖ Readability
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• ➖ Developer Documentation
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• ❌ Reviewed by human
• ❌ Code review by maintainers
• ❌ Full testing and approval
• ➖ Credit contributors
• ➖ Review with the product owner
• ❌ Release notes snippet
• ❌ Release

User interface changes

• After finishing the browser installer the site lands on /admin/dashboard/welcome rather than //admin/dashboard/welcome.

API changes

• N/A

Data model changes

• N/A

Release notes snippet

• Fixed the post-install redirect landing on a doubled slash.