✨ feat: Add custom request body editor with persistent message storage

- 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

web/src/components/playground/DebugPanel.js

@@ -24,6 +24,7 @@ const DebugPanel = ({
   onActiveDebugTabChange,
   styleState,
   onCloseDebugPanel,
+  customRequestMode,
 }) => {
   const { t } = useTranslation();
 
@@ -128,6 +129,11 @@ const DebugPanel = ({
             <div className="flex items-center gap-2">
               <Eye size={16} />
               {t('预览请求体')}
+              {customRequestMode && (
+                <span className="px-1.5 py-0.5 text-xs bg-orange-100 text-orange-600 rounded-full">
+                  自定义
+                </span>
+              )}
             </div>
           } itemKey="preview">
             <CodeViewer