[Documentation] Add src/scripts/README.md (#2442)

src/scripts/README.md

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+# Scripts Directory Documentation
+
+This directory contains TypeScript code inherited from the legacy ComfyUI JavaScript frontend project. The code has been migrated from JavaScript to TypeScript while maintaining compatibility with the original functionality.
+
+When implementing new features, prefer using the new Vue3 system over the legacy scripts.
+
+## Key Components
+
+### ComfyApi (api.ts)
+
+Main API client class that handles communication with the ComfyUI backend. Provides methods for:
+
+- Queue management
+- Model operations
+- Extension handling
+- WebSocket communication
+- User data management
+
+### ComfyApp (app.ts)
+
+Core application class that manages:
+
+- Graph manipulation
+- Node management
+- Canvas interactions
+- Extension system
+- Workflow state
+
+### UI Components (ui/)
+
+Collection of reusable UI components including:
+
+- Buttons and button groups
+- Popups and dialogs
+- Draggable lists
+- Image previews
+- Menu system
+- Settings dialog
+
+## Integration with Vite
+
+All TypeScript exports are shimmed through Vite configuration to maintain compatibility with the legacy JavaScript codebase. The shimming logic can be found in `vite.config.mts`.
+
+## Legacy Compatibility
+
+This codebase maintains compatibility with the original [ComfyUI Legacy Frontend](https://github.com/Comfy-Org/ComfyUI_legacy_frontend) while providing TypeScript type safety and modern development features.
+
+For users wanting to fall back to the legacy frontend, use the command line argument:
+
+```bash
+--front-end-version Comfy-Org/ComfyUI_legacy_frontend@latest
+```