Fix default configs and StarterKit script to support varbase_default_content for Vartheme BS5 only

Problem/Motivation

When generating themes using the StarterKit script, some configuration issues arise due to overlap with varbase_default_content. This results in missing elements such as:

• Social share icons
• Footer copyright message

These issues occur because the default content is meant only for the Vartheme BS5 base theme, but the current StarterKit behavior applies it even to generated custom themes, where it doesn't belong.

Proposed resolution

• Updated the StarterKit script to conditionally support varbase_default_content only for the Vartheme BS5 base theme.
• Prevented configuration pollution in generated themes.
• Fixed missing assets and content for:
  • Social share icons
  • Footer message
• Updated all relevant .stories.json files to align with the corrected default configurations and content expectations.

This ensures a clean developer experience with properly initialized content for Vartheme BS5, while keeping custom themes free from unnecessary or broken default content dependencies.

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 and Update Helper on new feature change/addition
• ❌ Release varbase-10.1.0-alpha2, vartheme_bs5-4.0.0-alpha7

Varbase update type

• ✅ No Update
• ➖ Optional Update
• ➖ Forced Update
• ➖ Forced Update if Unchanged

User interface changes

• N/A

API changes

• N/A

Data model changes

• N/A

Release notes snippet

• Issue #3539482: Fixed default configs and StarterKit script to support varbase_default_content for Vartheme BS5 only