feat: configure error page

[ahmtslmngcl]

This branch implements a common error page to display when an error occurs

Changes introduced:

• Adjusted error.tsx file with custom styling
• Added not-available.tsx for handling 404 errors
• Added buttons for navigating back to home and/or trying to re-render via built-in reset() function

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• adds topbar without the chatbot to the pages
• uses custom designs (button, text etc.)
• supports mobile and desktop

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