fix(landing): improve cursor visibility, contrast & responsiveness

[Rashi1404]

Description

Fixes UI/UX issues on the landing page reported in #1446.

Changes Made

• Cursor Visibility: Increased MouseSpotlight opacity from 0.05 to 0.18 and added a className="mouse-spotlight" for CSS targeting. The spotlight now remains visible on both light and dark backgrounds.
• Text Contrast: Fixed hero heading gradient from hardcoded white (#fff) to var(--foreground) — this ensures the "YOUR CODE HAS A" text is readable across all themes (dark, light, nordic, cyberpunk).
• Badge Styling: Updated "OPEN SOURCE • FREE FOREVER" badge to use color-mix(in srgb, var(--accent) 15%, transparent) for background and color-mix(in srgb, var(--accent) 40%, transparent) for border — theme-aware and clearly visible.
• Description Text: Changed from var(--muted-foreground) to var(--foreground) with opacity: 0.85 for better readability while maintaining visual hierarchy.
• Responsive Spacing: Changed hero section top padding from fixed 80px to clamp(100px, 12vh, 140px) for better mobile responsiveness and navbar clearance.
• Secondary CTA: Fixed "Star on GitHub" button text color from var(--muted-foreground) to var(--foreground) for sufficient contrast.
• Accessibility: Added landing-page specific focus-visible styles using var(--accent) for keyboard navigation, and replaced orphaned .custom-cursor CSS with properly scoped .lnd-root .mouse-spotlight.

Screenshots

before

after

Testing

• Cursor visible on all sections (light & dark themes)
• Text contrast meets WCAG AA standards (4.5:1 ratio)
• Responsive on mobile (320px), tablet (768px), desktop (1440px)
• Keyboard navigation focus indicators visible
• Tested with classic-dark, modern-light-blue, nordic-frost, cyberpunk-matrix themes

Related Issue

Closes #1446

[github-actions]

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[Rashi1404]

@Priyanshu-byte-coder
kindly add more labels