Add comprehensive watchOS app documentation

- Add watch-app-setup.mdx: Complete step-by-step guide to creating watchOS apps
- Add examples.mdx: Real-world examples (fitness tracker, smart home, notifications)
- Update index.mdx: Add documentation links and SwiftUI card
- Update tutorial: Add watchOS app creation section with code examples

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: riderx