phsl / new-api

- Add real-time request body preview that updates when parameters change
- Implement pre-constructed payload generation for debugging without sending requests
- Add support for image URLs in preview payload construction
- Upgrade debug panel to card-style tabs with custom arrow navigation
- Add collapsible functionality and dropdown menu for tab selection
- Integrate image-enabled messages with proper multimodal content structure
- Refactor tab state management with internal useState and external sync
- Remove redundant status labels and clean up component structure
- Set preview tab as default active tab for better UX
- Maintain backward compatibility with existing debug functionality

This enhancement significantly improves the debugging experience by allowing
developers to see exactly what request will be sent before actually sending it,
with real-time updates as they adjust parameters, models, or image settings.