Add a features section and responsive mobile layout to the landing page
The landing page (`example/index.html`) is a basic skeleton. It needs improvements to feel more complete:
- Add a "Features" section below "How it works" highlighting what Issue Scout provides (e.g. entry points, pattern detection, risk identification)
- Make the layout responsive — the `.steps` flex container breaks on narrow screens
- Add a "Get Started" or "Try it" section with usage instructions
- The CTA button has no link — connect it to the AI Catalog URL
- Add meta description and Open Graph tags for sharing
Acceptance criteria:
- [ ] Features section with at least 3 feature cards
- [ ] Page looks good on mobile (< 768px)
- [ ] CTA button links somewhere meaningful
- [ ] Meta tags added to `<head>`
issue