refactor(web): convert from styled-components to Tailwind CSS

[Copilot]

Addresses feedback from #1433 to migrate MobileGate component from styled-components to Tailwind CSS utility classes.

Changes

• Removed styled-components: Eliminated 5 styled component definitions (Container, Card, Title, Message, WaitlistButton) and replaced with inline Tailwind classes
• Semantic color tokens: Replaced hardcoded #a0a0a0 with text-text-light-inactive from the project's design system
• Code reduction: 89 lines → 30 lines while maintaining identical functionality

Before/After

// Before
const Message = styled.p`
  font-family: "Rubik", sans-serif;
  font-size: 16px;
  font-weight: 400;
  color: #a0a0a0;
  margin: 0 0 ${({ theme }) => theme.spacing.xl};
  line-height: 1.6;
`;

// After
<p className="mb-8 font-sans text-base leading-relaxed text-text-light-inactive">

All tests pass. Component appearance and accessibility unchanged.

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[tyler-dane]

Added changes manually