phsl / new-api

- Add CustomRequestEditor component with JSON validation and real-time formatting
- Implement bidirectional sync between chat messages and custom request body
- Add persistent local storage for chat messages (separate from config)
- Remove redundant System Prompt field in custom mode
- Refactor configuration storage to separate messages and settings

New Features:
• Custom request body mode with JSON editor and syntax highlighting
• Real-time bidirectional synchronization between chat UI and custom request body
• Persistent message storage that survives page refresh
• Enhanced configuration export/import including message data
• Improved parameter organization with collapsible sections

Technical Changes:
• Add loadMessages/saveMessages functions in configStorage
• Update usePlaygroundState hook to handle message persistence
• Refactor SettingsPanel to remove System Prompt in custom mode
• Add STORAGE_KEYS constants for better storage key management
• Implement debounced auto-save for both config and messages
• Add hash-based change detection to prevent unnecessary updates

UI/UX Improvements:
• Disabled state styling for parameters in custom mode
• Warning banners and visual feedback for mode switching
• Mobile-responsive design for custom request editor
• Consistent styling with existing design system