Add URL-Shrotener in Javascript

[psy-duck1]

🎯 What this PR does

• Adds a complete URL shortener built with vanilla JavaScript
• Includes modern, responsive UI with gradient design
• Implements localStorage for data persistence
• Features URL validation, click tracking, and copy-to-clipboard
• Supports automatic redirection and recent URLs management
• Fixes Add URL Shortener Project in Javascript #73

✨ Features Added

• ✅ URL validation and error handling
• ✅ Short code generation (6-character unique codes)
• ✅ Local storage persistence
• ✅ Click tracking and analytics
• ✅ Copy to clipboard functionality
• ✅ Recent URLs management
• ✅ Responsive design for all devices
• ✅ Modern UI with smooth animations

🧪 Testing

• Tested locally with Python HTTP server
• All functionality working as expected
• Responsive design verified on different screen sizes

📁 Files Added

• index.html - Main HTML structure
• script.js - JavaScript functionality
• style.css - Modern styling
• README.md - Comprehensive documentation
• .gitignore - Git ignore rules