Fix mobile responsiveness for landing page

[vrajnish336-afk]

Closes #3

This PR implements the requested mobile responsiveness for the LandingPage.tsx component while maintaining the original design system and Tailwind styling.

Changes Implemented

• Navbar: Adjusted spacing and typography to prevent horizontal overflow on small screens.
• Hero CTA & Bottom CTA: Updated responsive flex behavior so buttons stack vertically on mobile and remain side-by-side on larger screens.
• Tools Grid: Changed the responsive grid to one column on very small screens, two columns on tablets, and four columns on desktop.

Validation Performed

• Visual testing passed at 320px, 375px, 390px, 430px, 768px, and 1280px.
• npm run build passed successfully.
• Only frontend/src/pages/LandingPage.tsx was modified.

Note: Pre-existing lint and test failures outside the scope of this responsive layout update were not modified.