Expand Create a Page guide with comprehensive page context types documentation (#107)

Added detailed sections covering all available page context types:
- Assistant Page Context
- Backups Page Context
- Certificate Page Context
- Exports Page Context
- Intercept Page Context (with request/response/websocket selections)
- WebSocket Page Context

Each context type now includes:
- Description of what the context provides
- Code examples showing how to access the context
- Practical example of creating a page for that context type
- Clear explanations of page-specific state

Also added a new "Working with Page Context and State" section with best practices:
- Checking context availability
- Handling selection changes
- Updating UI reactively
- Providing fallback UI
- Proper listener cleanup

This expansion makes the guide comprehensive for developers building context-aware pages for different sections of Caido.

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Claude Haiku 4.5 <noreply@anthropic.com>

Author: 3 people