feat: make landing page fully responsive for mobile devices

[wanli132650]

Summary

This PR makes the landing page fully responsive for mobile devices, addressing all the issues mentioned in #3.

Changes Made

Navigation

• Added hamburger menu (Menu/X icons) for mobile screens
• Nav links hidden on small screens, shown in dropdown when menu is toggled
• Mobile menu closes when a link is clicked

Hero Section

• Reduced padding on mobile (px-4 instead of px-6, smaller pt/pb values)
• Reduced gap between grid items on mobile
• Slightly smaller button padding on mobile

Tools Grid

• Grid goes to single column on very small screens, 2 columns on xs breakpoint
• Added overflow-hidden and truncate for card content
• Slightly reduced padding on mobile cards

Steps Section

• Icon containers reduced from w-12/h-12 to w-10/h-10 on mobile
• Icon sizes reduced on mobile
• Gap reduced on mobile
• Text sizes responsive (text-sm on mobile, text-base on desktop)

CTA Section

• Reduced padding on mobile
• Title clamp minimum reduced for smaller screens
• Leading increased slightly on mobile for readability
• Button padding reduced on mobile

Footer

• Stacks vertically on mobile (flex-col)
• Centered text on mobile, left-aligned on desktop
• Reduced padding on mobile

Fixes #3