fix(layout): correct banner and vertical bar in demo mode

[jplanckeel]

Description

• Import useRef and useEffect hooks for DOM measurement and lifecycle management
• Add ResizeObserver to dynamically measure banner container height
• Convert banner container to fixed positioning with z-index layering
• Adjust sidebar positioning to account for banner height using dynamic top offset
• Adjust main content area padding to prevent overlap with fixed banners
• Ensure responsive layout recalculates when banner dimensions change
• Improve visual hierarchy and prevent content occlusion under sticky banners

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Test A
• Test B

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules