Update error pages

[damsfx]

This pull request updates the 404.html and 500.html error page templates to improve their appearance, responsiveness, and maintainability. The changes modernize the layout, enhance accessibility, and unify the branding and SVG usage across both pages.

Styling and Layout Improvements:

• Added a responsive <meta name="viewport"> tag and reworked the CSS to use flexbox for centering, improved font scaling with clamp(), and better color handling for both light and dark modes. This ensures the error pages look good on all devices and respect user preferences.

• Moved inline styles into a <style> block for maintainability and consistency, and removed redundant or outdated inline style attributes from HTML elements.

SVG and Branding Consistency:

• Updated the SVG logo markup in 500.html to match the more modern and maintainable structure from 404.html, using consistent class names and gradient definitions. This unifies the branding and reduces code duplication.

These updates collectively provide a more polished, user-friendly, and maintainable error page experience.-update dark scheme rendering