[Phase 4] Create landing page with pricing

## Description
Static landing page: feature overview, pricing tiers, CTA to sign up, SEO-optimized.

## Acceptance Criteria
- [ ] Landing page loads in under 3 seconds
- [ ] Feature overview section
- [ ] Pricing comparison table (free/pro/enterprise)
- [ ] Sign-up CTA
- [ ] SEO meta tags for documentation scraping API keywords

## Feature
Feature: F004 / Phase: 4