[docs] Add README for js directory (#1853)

* [docs] Add README for js directory

* [docs] Update js/README.md based on PR review feedback

* [docs] Update js/README.md with corrected descriptions

js/README.md

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+# ComfyUI-Manager: Frontend (js)
+
+This directory contains the JavaScript frontend implementation for ComfyUI-Manager, providing the user interface components that interact with the backend API.
+
+## Core Components
+
+- **comfyui-manager.js**: Main entry point that initializes the manager UI and integrates with ComfyUI.
+- **custom-nodes-manager.js**: Implements the UI for browsing, installing, and managing custom nodes.
+- **model-manager.js**: Handles the model management interface for downloading and organizing AI models.
+- **components-manager.js**: Manages reusable workflow components system.
+- **snapshot.js**: Implements the snapshot system for backing up and restoring installations.
+
+## Sharing Components
+
+- **comfyui-share-common.js**: Base functionality for workflow sharing features.
+- **comfyui-share-copus.js**: Integration with the ComfyUI Opus sharing platform.
+- **comfyui-share-openart.js**: Integration with the OpenArt sharing platform.
+- **comfyui-share-youml.js**: Integration with the YouML sharing platform.
+
+## Utility Components
+
+- **cm-api.js**: Client-side API wrapper for communication with the backend.
+- **common.js**: Shared utilities and helper functions used across the frontend.
+- **node_fixer.js**: Utilities for fixing disconnected links and repairing malformed nodes by recreating them while preserving connections.
+- **popover-helper.js**: UI component for popup tooltips and contextual information.
+- **turbogrid.esm.js**: Grid component library - https://github.com/cenfun/turbogrid
+- **workflow-metadata.js**: Handles workflow metadata parsing, validation and cross-repository compatibility including versioning, dependencies tracking, and resource management.
+
+## Architecture
+
+The frontend follows a modular component-based architecture:
+
+1. **Integration Layer**: Connects with ComfyUI's existing UI system
+2. **Manager Components**: Individual functional UI components (node manager, model manager, etc.)
+3. **Sharing Components**: Platform-specific sharing implementations
+4. **Utility Layer**: Reusable UI components and helpers
+
+## Implementation Details
+
+- The frontend integrates directly with ComfyUI's UI system through `app.js`
+- Dialog-based UI for most manager functions to avoid cluttering the main interface
+- Asynchronous API calls to handle backend operations without blocking the UI
+
+## Styling
+
+CSS files are included for specific components:
+- **custom-nodes-manager.css**: Styling for the node management UI
+- **model-manager.css**: Styling for the model management UI
+
+This frontend implementation provides a comprehensive yet user-friendly interface for managing the ComfyUI ecosystem.