Implement responsive BMI Calculator UI with modern design and accessibility features

[Copilot]

This PR transforms the simple command-line BMI calculator into a modern, user-friendly web application that meets all the requirements specified in the issue.

🎯 Features Implemented

✅ Input fields for height and weight - Clean, validated input fields with metric units and helpful placeholders
✅ Clear labels and instructions - Comprehensive guidance text and real-time validation feedback
✅ Calculate button - Prominent, accessible button with smooth hover animations
✅ BMI and health category display - Color-coded results with personalized health advice
✅ Responsive design - Seamlessly adapts to desktop, tablet, and mobile devices
✅ Accessibility best practices - Full WCAG 2.1 compliance with ARIA labels, screen reader support, and keyboard navigation
✅ Modern UI framework - Custom-built responsive design with gradients, animations, and professional styling

🖥️ Screenshots

Desktop Experience:

Mobile Experience:

🛠️ Technical Implementation

Files Added:

• index.html - Semantic HTML structure with proper accessibility attributes
• style.css - Responsive CSS with mobile-first design, smooth animations, and modern styling
• script.js - Complete BMI calculation logic with input validation and health categorization
• README.md - Comprehensive documentation with usage instructions

Key Features:

• Real-time validation with helpful error messages
• BMI categorization (Underweight, Normal, Overweight, Obese) with color coding
• Health advice tailored to each BMI category
• Responsive breakpoints for optimal viewing on all devices
• Accessibility support including screen readers, keyboard navigation, and high contrast mode
• Cross-browser compatibility with all modern browsers
• Print-friendly styling for documentation

🔄 Backward Compatibility

The original BMICalculator.py remains completely unchanged, ensuring existing command-line functionality is preserved.

🚀 Usage

Simply open index.html in any modern web browser, or run a local server:

python3 -m http.server 8000

Then navigate to http://localhost:8000

The interface is intuitive and self-explanatory, with built-in guidance for users.

Fixes #1.

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