Transform Main Menu into Vertical Collapsible Sidebar with Responsive Design

The main menu has been transformed from a horizontal layout to a vertical, collapsible sidebar. Key changes include:

Adjusted the sidebar's collapse behavior to ensure proper functionality and appearance.
Improved responsive design and ensured the menu remains functional on various devices.
Removed 'By Industry' and 'By Role' categories and renamed 'Solutions' to 'Use Cases'.
Refined the menu structure to ensure consistent indentation and added submenus for various sections.
Enhanced the sidebar's appearance with custom scrollbar styling featuring a fade effect and semi-transparent spherical sliders.
Updated the logo placement and ensured it remains visible when the menu is collapsed.
Ensured the entire menu item lines are clickable to expand or collapse submenus.
Positioning the mobile toggle button below the logo for better accessibility.
Updated footer content with required copyright text.

Please review the changes and ensure everything works as expected across different browsers and screen sizes.

Tips:

Make sure to test changes before merging.
Submit a "Request Changes" review and I'll address it.
Close this PR with a comment if it's obviously incorrect. This will improve my future PRs.
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yanok-stage / www.yanok.ai