imporve frontend

Added null-checks for all DOM elements to prevent JS errors on missing elements.

Added fallback for IntersectionObserver to support older browsers.

Improved particlesJS handling with a safe fallback message if it’s unavailable.

Fixed mobile menu added missing .open styles in CSS for proper toggle visibility.

Enhanced form submission feedback restored SVG safely and added basic accessibility updates.

Smoothed cursor outline animation for better UX.

Cleaned up event listeners/observers to avoid memory leaks.

Improved form error handling (replaced alert with structured message).