feat: comprehensive mobile-responsive landing page

[xu675693517-hue]

Changes

Mobile navigation

• Added hamburger menu (Menu/X icons) for screens <640px
• Desktop nav links hidden on mobile, shown in dropdown menu
• Brand logo text resizes responsively

Hero section

• Reduced padding: py-12 on mobile vs py-20 desktop
• Font size clamp starts at 1.8rem (was 2.2rem)
• CTA buttons stack vertically on mobile with justify-center
• Spacing tightened: mt-5/mt-8 on mobile

Tools grid

• 1 column <400px (new xs breakpoint), 2 cols 400-640px, 4 cols >640px
• Card padding and text sizes scale down on mobile
• Gap reduced from gap-3 to gap-2 on small screens

How it works

• Padding: py-16 mobile, py-32 desktop
• Icon containers: w-10/h-10 mobile, w-12/h-12 desktop
• Text sizes and gaps reduced proportionally

CTA section

• Padding: py-16 mobile vs py-28 previously
• Buttons stack vertically on mobile
• Title font size clamp starts at 1.8rem

Footer

• Stacks vertically on mobile, centered text

Ambient glow

• Fixed overflow on mobile using min() CSS for width/height

Crystal prism

• Uses min(340px, 70vw) to scale with viewport

Tailwind config

• Added xs: 400px breakpoint for very small screen support

Testing

• TypeScript compilation: zero errors
• Vite build: passes
• Dev server: confirmed serving correctly

Closes #3