Add light/dark theme switcher with web interface for Azure SDK documentation

[Copilot]

This PR adds a comprehensive light/dark theme switcher to the Azure SDK UX study repository by creating a modern web interface to display the documentation content.

What was added

Since the repository contained only markdown documentation files, I created a complete web application to showcase the Azure SDK documentation with theme switching capabilities:

🎨 Theme Switcher Features

• Toggle Button: Circular button in the header with intuitive moon/sun icons
• Theme Persistence: User preference saved to localStorage and restored on page reload
• System Theme Detection: Automatically detects user's system preference as fallback
• Smooth Transitions: All theme changes include CSS transitions for professional UX

🌐 Web Interface

• Modern Layout: Clean, professional design with sticky navigation
• Responsive Design: Adapts seamlessly to mobile and desktop screens
• Accessibility: Full keyboard navigation, ARIA labels, and reduced motion support
• Documentation Display: Organized presentation of Azure SDK quickstart and VM tutorial content

🎯 Technical Implementation

• CSS Custom Properties: Theme variables for consistent color management
• JavaScript Classes: Modular code organization for maintainability
• LocalStorage API: Persistent theme preference storage
• Media Queries: Responsive breakpoints and system theme detection

Screenshots

Light Theme:

Dark Theme:

Mobile Dark Theme:

How to use

1. Open index.html in a web browser or serve with a local HTTP server
2. Click the theme toggle button (🌙/☀️) in the top-right corner to switch themes
3. Your theme preference will be automatically saved and restored on future visits
4. Use the navigation links to jump to different sections of the documentation

The interface provides an enhanced user experience for consuming Azure SDK documentation while demonstrating modern web development practices for theme management.

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