feat: mobile responsive layout for all pages

[EmeditWeb]

Problem

The web app is designed for desktop. On mobile
screens the layout breaks, content overflows,
and buttons are too small to tap.

What To Build

Audit every page and fix mobile responsiveness:

• Navbar: hamburger menu on mobile (already in Navbar.tsx,
  verify it works)
• Home: hero text size, CTA buttons stack vertically,
  feature cards single column
• Dashboard: role cards stack vertically
• Sponsors: pool stats wrap, forms full width
• Vendors: grid becomes single column
• Vouch: tabs become full width, cards stack

Test at 375px (iPhone SE), 390px (iPhone 14),
768px (iPad).

Files To Touch

All page files in src/pages/
src/components/layout/Navbar.tsx

Acceptance Criteria

• No horizontal scroll on any page at 375px
• All buttons tappable (min 44px height)
• Text readable without zoom
• Forms usable on mobile keyboard

Mandatory Checks Before PR

• npm run build passes
• Tested at 375px viewport
• PR references this issue